You want your child’s birthday to be the party everyone’s still talking about at school on Monday. And honestly? An Under the Sea birthday party is your golden ticket.
It’s colorful. It’s magical. It works for toddlers AND older kids. And it gives you endless room to get creative with decorations, food, activities, and favors – all without blowing your budget.
Whether you’re going for soft pastels and mermaids or bold blues and sharks, this theme is endlessly customizable. The best part? Most of these ideas are easy to DIY, easy to find online, and guaranteed to wow every kid (and parent) in the room.
We’ve rounded up 45 of the best Under the Sea birthday party ideas – from showstopping decor to adorable treats – so you can plan the ultimate underwater adventure for your little one.
Let’s dive in!
🎉 Why an Under the Sea Party Theme is Always a Hit
Before we get into the ideas, here’s why this theme works so well:
It appeals to all ages. Toddlers love the colorful fish and mermaids. Older kids go wild for treasure hunts and shark décor. You literally can’t go wrong.
The color palette is stunning. Blues, teals, corals, and purples – your party photos are going to look incredible.
It’s flexible. Want a dreamy mermaid vibe? Done. Prefer a Nemo-inspired look? Easy. Going for a dramatic deep-sea aesthetic? Absolutely.
Now, let’s get into the good stuff.
🐟 Under the Sea Party Decorations
1. Jellyfish Lanterns
These are the showstopper of any Under the Sea party, and guests always gasp when they walk in.
Hanging jellyfish lanterns transform your ceiling into an actual ocean – and they’re so much easier to make than they look.
What You’ll Need:
- Round paper lanterns in blue, white, and teal (various sizes)
- Curling ribbon or crepe paper streamers in matching colors
- String or fishing line for hanging
- Optional: battery-operated fairy lights inside each lantern
How to Make It:
1. Open each paper lantern and hang from the top hook.
2. Cut ribbon or streamers into strips of varying lengths (about 18–24 inches each).
3. Bunch the strips together and tape or tie them to the bottom of the lantern to create tentacles.
4. Curl the ribbon by running it along the edge of scissors.
5. Hang from the ceiling at different heights using fishing line for a floating effect.
Pro Tip: Use white fairy lights inside each lantern for a magical glowing jellyfish effect – especially beautiful for an evening party.
2. Rainbow Balloon Clam Shell Backdrop
This is THE statement piece that makes every party photo look like it belongs in a magazine. A giant clam shell outline filled with rainbow balloons becomes an instant photo booth backdrop your guests will line up to photograph in front of.
What You’ll Need:
- A large wooden or foam board cut into a clam shell shape (or purchase a pre-cut backdrop frame)
- Balloons in pastel rainbow colors (pink, peach, cream, mint, teal)
- Balloon pump
- Low-temp hot glue or balloon tape strips
- Optional: fringe curtain or iridescent streamers for background
How to Make It:
1. Build or purchase your clam shell backdrop frame – cardboard works great for DIY.
2. Inflate balloons to varying sizes for a natural organic look.
3. Starting from the bottom, hot glue or tape balloons row by row inside the shell frame.
4. Work upward, blending colors gradually from teal at the base to pinks and peaches at the top.
5. Fill in any gaps with smaller balloons for a full, lush look.
6. Place in front of your party table as the ultimate dessert table backdrop.
Pro Tip: Add iridescent fringe curtains behind the backdrop for extra shimmer and depth in photos.
3. Seashell-Shaped Party Plates
Skip the plain round plates – seashell-shaped party plates are a small detail that makes a big impact on your table styling. They come in white, pink, and iridescent finishes that perfectly match the ocean theme.
What You’ll Need:
- Seashell-shaped paper or compostable plates (available on Etsy and Amazon)
- Coordinating napkins in blue, teal, or blush
- Optional: iridescent charger plates underneath for extra glam
How to Use It:
1. Layer a larger iridescent charger on the bottom.
2. Place the seashell plate on top.
3. Add a smaller shell-shaped snack plate if desired.
4. Tuck a rolled napkin tied with twine or a ribbon alongside it.
Pro Tip: Scatter real or faux seashells and star-shaped confetti across the table to complete the look.
4. Foil Sea Animal Balloons
Giant foil balloons shaped like dolphins, octopuses, seahorses, and turtles floating above your party tables take the theme to the next level – no extra decorating needed around them.
What You’ll Need:
- Foil balloons in sea creature shapes (dolphins, fish, sharks, sea turtles)
- Helium tank or helium balloon service
- Curling ribbon in coordinating colors
- Balloon weights or sturdy anchors
How to Set It Up:
1. Inflate foil balloons with helium.
2. Attach curling ribbon and curl it for a fun floating effect.
3. Anchor to balloon weights at the center of each table, or tie to the backs of chairs.
4. Mix with regular blue and teal latex balloons for a full, layered look.
Pro Tip: A giant dolphin or shark foil balloon makes an incredible photo backdrop on its own. Place one near the entrance for a wow moment as guests arrive.
5. Clam Shell Photo Prop
An inflatable giant clam shell is a genius photo prop that also doubles as a seat – and it’s the kind of detail that makes parents say “Where did you find that?!”
What You’ll Need:
- Giant inflatable clam shell (available on Amazon and party supply sites)
- Pastel balloon cluster to arrange beside it
- A small balloon garland using a balloon tape strip
How to Set It Up:
1. Inflate the clam shell and place it in a prominent spot – outdoors on grass looks stunning.
2. Build a small balloon garland using pastel colors and attach it alongside the shell.
3. Place a small starfish or faux gold coin inside the shell for an extra whimsical detail.
4. Set up a phone tripod nearby so parents can easily snap photos of kids sitting inside.
Pro Tip: This also doubles as a fun seat for the birthday child during cake time – perfect for that iconic birthday photo.
6. Scalloped Tablescape Plating
A scalloped-edge table setup – think scalloped plates, scalloped napkins, and layered ocean tones – gives your party table a polished, dreamy look that photographs beautifully.
What You’ll Need:
- Scalloped-edge paper plates in blue, blush, or white
- Scalloped napkins
- Small bud vases with baby’s breath or simple florals
- Starfish and shell scatter decor
How to Style It:
1. Lay a pastel tablecloth as your base – blush pink or sky blue work beautifully.
2. Layer scalloped plates – large on bottom, smaller on top.
3. Add a scalloped napkin folded to the side.
4. Place mini bud vases with wildflowers or baby’s breath as simple centerpieces.
5. Scatter starfish and tiny shells casually down the center of the table.
Pro Tip: Add a small name card in front of each place setting for an extra-special personalized touch.
7. Pastel Mermaid Party Setup
Soft pinks, lavenders, and minty greens give this theme a dreamy, ethereal look – perfect if you want something a little more elegant and less “bright primary colors.”
What You’ll Need:
- Pastel balloons in pink, lavender, mint, and white
- Iridescent or holographic streamers
- Mermaid scale-print backdrop or tablecloth
- Iridescent tableware
How to Set It Up:
1. Hang iridescent streamers vertically across your main party wall to create a shimmery curtain effect.
2. Build a soft pastel balloon garland to frame the dessert table.
3. Use mermaid scale-print wrapping paper as a quick DIY table runner.
4. Pair with holographic tableware for a cohesive, magical look.
Pro Tip: This pastel palette is absolutely gorgeous for a “Little Mermaid” or “mermaid birthday” theme and photographs beautifully in natural light.
8. Blue and White Classic Under the Sea Setup
Sometimes keeping it clean and simple is the most stunning choice. A crisp blue and white color palette looks fresh, polished, and totally on-theme without needing a ton of extra decorations.
What You’ll Need:
- White tablecloths with blue table runners
- Blue and white balloons (mix of sizes)
- White ceramic or paper plates
- Blue glass or plastic cups
- White coral or starfish centerpieces
How to Set It Up:
1. Layer white tablecloths with striped or solid blue runners down the center.
2. Create tall balloon columns using blue and white balloons as anchor pieces at each end of the table.
3. Use white ceramic or paper plates for an elevated look.
4. Place small white coral branches or starfish in clear glass vases as centerpieces.
Pro Tip: Add touches of silver or gold – like gold starfish scatter or silver utensils – to elevate the whole setup and make it feel extra special.
9. Balloon Bubble Arch
Clear “bubble” balloons mixed into a regular balloon garland create the most stunning underwater effect – it genuinely looks like bubbles floating up from the ocean floor.
What You’ll Need:
- Clear or transparent balloons in various sizes
- Blue, teal, and white latex balloons
- Balloon tape strip
- Fishing line or balloon arch frame
How to Make It:
1. Inflate clear balloons to different sizes to mimic actual bubbles.
2. Build a base garland with blue and teal balloons using balloon tape.
3. Tuck clear balloons throughout the garland, especially toward the top.
4. Arch over a doorway, dessert table, or photo backdrop area.
Pro Tip: Add a confetti-filled clear balloon or two for extra sparkle – it looks incredible in photos.
10. Under the Sea Party Table
Your party table is the centerpiece of the whole event, and an ocean-themed table with coordinated plates, cups, napkins, and centerpieces ties the entire look together in one gorgeous spread.
What You’ll Need:
- Ocean-themed party tableware set (Meri Meri makes stunning options)
- Blue textured or foil tablecloth
- Coral and shell centerpiece pieces
- Ocean-colored cups and straws
How to Style It:
1. Lay a blue textured or crinkle-foil tablecloth for that “under the sea floor” effect.
2. Set each place with coordinating plates, cups, and napkins from the same collection.
3. Create a centerpiece with colorful faux coral pieces, shells, and starfish in a shallow dish.
4. Add ocean-themed party favors at each place setting so kids have something to look at (and touch) during the party.
Pro Tip: Look for party tableware sets that come as a complete matching collection – it saves you time coordinating and keeps the look polished.
11. Fish Tail Balloon Garland
This whimsical balloon installation features a giant mermaid tail silhouette made entirely from balloons – it’s creative, eye-catching, and surprisingly achievable at home.
What You’ll Need:
- Balloons in teal, aqua, mint, and iridescent
- Balloon tape strip
- Fishing line for hanging
- A printed or hand-drawn mermaid tail template for reference
How to Make It:
1. Using balloon tape, create the base body of the tail shape with large teal and aqua balloons.
2. Use smaller balloons to fill in the fin detail at the bottom.
3. Add iridescent or clear balloons throughout for a shimmery, scaly effect.
4. Hang from the wall or ceiling as a statement wall installation.
Pro Tip: This looks absolutely spectacular as a backdrop behind the birthday cake table.
12. Mermaid Tail Table Runners
Iridescent mermaid tail-shaped table runners – or even mermaid tail fabric lengths – make your tables look like they came straight out of a fairytale.
What You’ll Need:
- Iridescent or holographic fabric or pre-made mermaid tail runners (Etsy has gorgeous options)
- Coordinating solid-color tablecloth as a base
- Scatter shells and confetti on top
How to Style It:
1. Lay your base tablecloth first.
2. Drape the mermaid tail runner down the center of the table.
3. Scatter faux pearl beads, shells, and star-shaped glitter on top.
4. Place centerpieces on top of the runner for a cohesive look.
Pro Tip: This is an easy, low-effort way to add major visual impact to your table without spending a lot of money.
13. Deep Sea Backdrop
A dramatic deep-sea backdrop – deep navy, teal, and dark aqua tones with silhouettes of sea creatures – creates a moody, immersive underwater world effect that looks incredible in party photos.
What You’ll Need:
- A printed deep-sea photo backdrop (available on Amazon and Etsy) OR navy blue fabric
- Silver or glow-in-the-dark sea creature cut-outs to attach
- Balloon garland in navy, deep teal, and white
How to Set It Up:
1. Hang your printed backdrop or deep navy fabric across a wall.
2. Attach sea creature silhouettes or cut-outs scattered across the backdrop.
3. Build a balloon garland along the bottom to create an “ocean floor” effect.
4. Add a simple table in front for the cake display.
Pro Tip: This darker palette works beautifully for older kids and evening parties – it feels more sophisticated than the typical bright-blue setup.
14. Paper Fan Ocean Decorations
Paper fans in shades of teal, blue, white, and coral hung on walls or ceilings add a festive, dimensional look that fills space beautifully without a huge budget.
What You’ll Need:
- Paper fan decorations in ocean colors (set of assorted sizes)
- Fishing line or string for hanging
- Command hooks or tape for attaching to walls or ceiling
How to Use It:
1. Mix fan sizes – large ones make a statement; smaller ones fill gaps nicely.
2. Create a cluster of fans on your main party wall at different heights.
3. Intersperse with balloon clusters and paper sea creature cut-outs for a layered effect.
4. Hang some from the ceiling as well for a 360-degree decorated feel.
Pro Tip: Paper fans are one of the most budget-friendly ways to fill a large wall space – a pack of 12 mixed-size fans can cover an entire wall beautifully.
15. Coral Reef Table Centerpiece
A DIY coral reef centerpiece – made from painted pasta, painted rocks, or faux coral branches – is a gorgeous and totally unique table focal point that kids will love touching and examining.
What You’ll Need:
- Faux coral branches (available at craft stores or Amazon) OR painted pasta in coral and white
- Clear glass vase or wide shallow bowl
- Aquarium sand or white sand for the base
- Small plastic sea creatures to nestle among the coral
How to Make It:
1. Fill the bottom of your vase or bowl with white or colored sand.
2. Press coral branches or painted pasta pieces into the sand to stand upright.
3. Nestle small plastic fish, starfish, and shells around the base.
4. Add a few glass pebbles or water beads for an extra aquarium feel.
Pro Tip: Make several small versions for each table rather than one large one – it keeps the theme consistent across all your tables.
16. Shark-Filled Waters Balloon Display
This one is a total hit with kids who love the shark vibe. Giant shark foil balloons swimming through a sea of blue and teal balloons is dramatic, fun, and seriously impressive.
What You’ll Need:
- Giant shark foil balloons (helium-filled)
- Large quantity of blue, teal, white, and orange latex balloons
- Balloon arch frame or balloon tape
- Fishing line for hanging foil sharks
How to Set It Up:
1. Build a large balloon cluster or arch using your blue and teal balloons as the base.
2. Inflate shark foil balloons with helium and tuck them INTO the balloon cluster so they appear to be swimming through.
3. Add white balloons to mimic foam and bubbles.
4. Pop in a few orange balloons for contrast – it makes the whole thing more dynamic.
Pro Tip: This theme is perfect for a “Baby Shark” party for toddlers or a “Shark Week” theme for older kids. Either way, it brings the energy!
17. Ocean Floor Ground Display
Don’t just decorate up – decorate down! Creating an “ocean floor” effect with blue fabric or cellophane, sand, shells, and sea creature toys along the floor of your party space adds an immersive layer most parties skip entirely.
What You’ll Need:
- Blue cellophane or light blue fabric
- Play sand or real sand in a contained area
- Plastic sea creature toys, shells, and starfish
- Optional: small aquarium plants
How to Set It Up:
1. Lay blue cellophane or fabric along the base of your dessert table or party backdrop.
2. Scatter shells, starfish, and plastic sea creatures on top.
3. If you’re outdoors, create a small sandbox “tide pool” kids can explore.
4. Add small aquarium plants to make it feel like a real ocean floor scene.
Pro Tip: This makes an incredible photo scene – lay it out at the base of your balloon arch or backdrop for a complete top-to-bottom ocean look.
18. Streamer Seaweed Wall
Long green and teal streamers hanging vertically from a curtain rod or doorframe creates the most fun seaweed effect – and kids absolutely love walking through it.
What You’ll Need:
- Green, dark teal, and blue crepe paper streamers
- Tension rod or dowel for your doorframe or wall
- Tape or zip ties to attach streamers to the rod
- Scissors to curl and rough up the edges
How to Make It:
1. Cut streamers to floor length (or longer so they pool slightly).
2. Attach to a tension rod or dowel using tape or zip ties, alternating green and teal.
3. Gently twist some streamers for a more organic, seaweed-like appearance.
4. Hang in a doorway or against a wall for guests to walk through or photograph in front of.
Pro Tip: Add a few blue streamers mixed in to create depth – it looks more like an actual underwater scene than pure green alone.
19. Swimming Fish Wall Décor
Colorful paper or foam fish cut-outs arranged in a “school” pattern across a wall creates a playful, vibrant display that’s perfect for younger children’s parties.
What You’ll Need:
- Foam or cardstock fish cut-outs in bright colors (pre-made or DIY)
- Washi tape or removable wall stickers to attach
- Optional: string and tape to hang some at different heights
How to Make It:
1. Cut fish shapes from colorful cardstock or purchase pre-made foam cut-outs.
2. Arrange them in a sweeping, flowing pattern across your party wall as if they’re swimming.
3. Vary sizes – larger fish in front, smaller ones in the background – for a sense of depth.
4. Add blue wave shapes and bubble cut-outs between the fish to fill the scene.
Pro Tip: Let kids decorate their own fish cut-out as an activity – then add their fish to the wall to make the display even more special and personalized.
20. Under the Sea Balloon Tunnel
Imagine your guests walking through an arch of blue and teal balloons into the party space – it sets the underwater mood from the very first second they arrive. This is the kind of entrance that makes kids gasp.
What You’ll Need:
- Balloon arch frame kit
- Blue, teal, white, and clear balloons
- Balloon pump
- Ribbon or greenery to fill any gaps
How to Make It:
1. Assemble your arch frame at the party entrance.
2. Inflate balloons in varied sizes and attach using balloon tape or directly to the frame.
3. Alternate colors – blue, teal, white – in an organic, natural pattern.
4. Tuck clear “bubble” balloons throughout for that underwater effect.
5. Add sea creature foil balloons at the top peak of the arch as a finishing touch.
Pro Tip: Balloon arches look more professional when you vary the sizes significantly – use a mix of 5-inch, 11-inch, and 16-inch balloons.
🐠 Under the Sea Party Favors
21. Pet Fish Favor Bags
Send kids home with a “pet fish” – a small toy fish or a beta fish-shaped candy inside a clear favor bag filled with blue cellophane “water.” It’s adorable, themed, and kids absolutely love it.
What You’ll Need:
- Clear treat bags
- Blue cellophane shred or blue tissue paper
- Small plastic fish toys or gummy fish candy
- Ribbon or twist ties to seal
- Optional: printed “Thanks for swimming by!” tag
How to Make It:
1. Fill the bottom third of the clear bag with blue cellophane shred to mimic water.
2. Place a small plastic fish or handful of gummy fish on top.
3. Add other small treats – fish crackers, ocean-themed stickers, a small shell.
4. Tie off with a blue ribbon and attach a “Thanks for swimming by!” card.
Pro Tip: Use actual small fish bowls (plastic) instead of bags for an extra creative twist – it takes the idea to the next level.
🍽️ Under the Sea Party Food & Treats
22. Starwiches (Star-Shaped Sandwiches)
Use a star-shaped cookie cutter to transform regular sandwiches into adorable “starfish” sandwiches. They’re cute, easy, and kids will eat them up without a fuss.
What You’ll Need:
- Sandwich bread (white or wheat)
- Your favorite sandwich fillings (PB&J, ham & cheese, or cream cheese)
- Star-shaped cookie cutter
How to Make It:
1. Make sandwiches as usual with your chosen filling.
2. Press the star cookie cutter firmly through each sandwich.
3. Arrange on a platter and optionally dust with a tiny sprinkle of sea salt for “sand.”
4. Label the platter “Starwiches” with a cute printed sign for extra charm.
Pro Tip: Use orange cheddar cheese inside for a more starfish-like color! You can also use cookie cutters in fish and shell shapes for variety.
23. Under the Sea Marshmallow Pops
Chocolate-dipped marshmallows decorated to look like sea creatures are an easy, crowd-pleasing treat that looks like you spent way more effort than you actually did.
What You’ll Need:
- Large marshmallows
- Lollipop sticks
- Blue or teal candy melts
- White candy melts
- Sprinkles, edible glitter, and candy eyes
How to Make It:
1. Push a lollipop stick into each marshmallow.
2. Melt candy melts according to package directions.
3. Dip each marshmallow pop into the melted candy, letting excess drip off.
4. While still wet, add candy eyes and decorate with ocean-themed sprinkles.
5. Stand upright in a styrofoam block to set completely.
Pro Tip: Use a combination of blue and white candy melts swirled together for a beautiful ocean wave effect on each pop.
24. Ocean Floor Charcuterie Board
Transform a standard snack board into an “ocean floor” scene with blue-tinted hummus as the “water,” crackers as “rocks,” and veggies and fruits arranged to look like a coral reef.
What You’ll Need:
- Large wooden or slate board
- Blue food coloring
- Hummus or cream cheese
- Crackers, veggies, fruits, cheese
- Star-shaped cookie cutter for cutting cheese shapes
- Small sea creature picks or toothpick flags for labeling
How to Make It:
1. Mix a drop of blue food coloring into your hummus or cream cheese and spread across the board as your “ocean.”
2. Arrange crackers and cheese slices in clusters to create a “coral reef” look.
3. Use star and fish-shaped cookie cutters on cheese slices for themed shapes.
4. Tuck veggies like broccoli as “seaweed” and carrot sticks as “coral.”
5. Add blueberries and grapes as “pebbles” in the corners.
Pro Tip: Place the whole board on a large piece of blue butcher paper with scattered shell cutouts for a fully immersive presentation.
25. Shark Attack Kids Mocktail
This is the drink every kid at the party will go crazy for – a layered blue-green lemonade with a gummy shark “attacking” the rim. It’s dramatic, delicious, and so on-theme.
What You’ll Need:
- Blue raspberry lemonade or blue sports drink
- Lemon-lime soda (Sprite or 7-Up)
- Blue food coloring (optional)
- Gummy sharks
- Clear plastic cups
- Fun straws
How to Make It:
1. Fill cups about halfway with blue lemonade or colored lemon-lime soda.
2. Slowly pour lemon-lime soda over the back of a spoon to create a layered effect.
3. Perch a gummy shark on the rim of the cup so it looks like it’s swimming toward the drink.
4. Add a fun striped or ocean-themed straw.
Pro Tip: Set up a self-serve “shark attack bar” where kids can build their own drinks – it doubles as an activity and they LOVE it.
26. Seafood Salad Hawaiian Rolls
Mini Hawaiian rolls filled with a simple tuna or mock seafood salad are a fun, easy-to-eat party food that fits the ocean theme perfectly – and they disappear fast.
What You’ll Need:
- Hawaiian sweet dinner rolls
- Canned tuna or imitation crab
- Mayo, celery, lemon juice, salt & pepper
- Optional: butter lettuce for lining
- Fish or seashell picks for serving
How to Make It:
1. Mix your tuna or crab with mayo, diced celery, a squeeze of lemon, and seasoning.
2. Slice Hawaiian rolls in half horizontally and lightly toast if desired.
3. Fill each roll generously with the seafood salad mixture.
4. Insert a decorative fish or shell pick into each roll before serving.
Pro Tip: Make a vegetarian version with smashed chickpea “salad” for non-seafood eaters – it tastes great and works for kids with allergies.
27. Pastel Ocean-Inspired Treats Spread
A coordinated dessert spread in soft pastel ocean tones – lavender macarons, mint cupcakes, blush cake pops – looks absolutely stunning on a party table and makes a gorgeous centerpiece.
What You’ll Need:
- Your choice of pastel-frosted cupcakes, macarons, cake pops, and cookies
- Blue, mint, and pink food coloring
- Edible glitter, pearl sprinkles, and iridescent sugar
- Tiered cake stand or display risers
How to Style It:
1. Bake or order treats in a coordinated pastel palette – mint, blush, lavender, and baby blue.
2. Decorate with ocean-inspired toppers: edible shells, starfish, and pearl sprinkles.
3. Arrange on a tiered stand, varying heights for visual interest.
4. Fill any gaps with small shells, confetti, or iridescent shred.
Pro Tip: Stick to a maximum of three colors in your treat spread – it’ll look more intentional and professional than using too many.
28. Seaweed Spirals
Cucumber spirals or green apple slices arranged to look like seaweed are a clever, healthy addition to your snack table that kids actually enjoy eating.
What You’ll Need:
- English cucumbers or green apples
- Spiralizer or sharp knife
- Blue serving platter
- Optional: green ranch dip alongside
How to Make It:
1. Use a spiralizer to create long, ribbon-like cucumber spirals – these look most like seaweed.
2. If no spiralizer, use a vegetable peeler to create long thin strips.
3. Arrange them in loose, wavy piles on a blue platter to mimic the motion of seaweed in water.
4. Serve with a green herb dip or ranch on the side.
Pro Tip: Label them “Seaweed Snacks” with a cute handwritten sign – kids find it way more fun to eat when there’s a silly name involved.
29. Mermaid Punch
A gorgeous blue-green layered punch that shimmers in the bowl – this is the most photogenic drink you’ll serve at the whole party. It looks magical and tastes even better.
What You’ll Need:
- Blue Hawaiian Punch or blue raspberry lemonade
- Lemon-lime soda
- Coconut or pineapple sherbet
- Edible silver glitter or luster dust
- Clear punch bowl
- Iridescent ladle
How to Make It:
1. Pour blue punch into the bowl as the base layer.
2. Slowly add lemon-lime soda around the edges – it creates a beautiful bubble effect.
3. Float scoops of coconut or pineapple sherbet on top.
4. Dust with edible glitter for shimmer right before serving.
5. Garnish with star-shaped fruit or blueberries floating on top.
Pro Tip: Freeze gummy fish or edible flowers into ice cubes beforehand – they’ll float in the punch bowl and look absolutely incredible.
30. Crab Sandwiches
Adorable little crab-shaped sandwiches – or grilled cheese cut into crab shapes – are a fun, kid-friendly food that looks amazing on the party spread and is easy to batch-make in advance.
What You’ll Need:
- Sandwich bread
- Your choice of fillings (grilled cheese, PB&J, or ham and cheese)
- Crab-shaped cookie cutter (or cut freehand with a sharp knife)
- Small candy eyes or olive slices for crab faces
How to Make It:
1. Prepare sandwiches with your filling of choice.
2. Use a crab cookie cutter to press firmly through the sandwich.
3. Add two small candy eyes on top using a dot of cream cheese to adhere.
4. Arrange on a platter with seaweed spiral garnish around them.
Pro Tip: For grilled cheese crabs, use orange American cheese for the most vibrant, crab-like color. The kids go absolutely wild for them.
31. Pastel Ocean-Inspired Cake
The birthday cake is the centerpiece of the whole party – and an ocean-inspired cake in soft pastels with fondant sea creatures on top looks stunning and makes the most unforgettable birthday photo.
What You’ll Need:
- 2-3 tier cake (bake yourself or order from a bakery)
- Buttercream in mint, blush, and white
- Fondant sea creature toppers OR edible wafer paper decorations
- Edible pearls and iridescent sprinkles
- Mermaid tail cake topper
How to Make It:
1. Frost each tier in a different pastel shade – mint on the bottom, blush in the middle, white on top.
2. Use an offset spatula to create a gentle “wave” texture in the frosting.
3. Apply edible pearls and silver sprinkles while the frosting is still soft.
4. Top with fondant sea creature decorations and a mermaid tail topper.
5. Add sugar coral branches around the base tiers for a reef effect.
Pro Tip: Can’t bake? Order a naked or semi-naked cake from a local bakery and just add the fondant toppers yourself – it looks custom-made at a fraction of the cost.
32. Seaweed Skewers
Green fruit and veggie skewers arranged to look like seaweed are a healthy, themed snack that fits perfectly on your ocean-themed food table – and they’re genuinely delicious.
What You’ll Need:
- Green grapes
- Honeydew melon balls or cubes
- Kiwi slices
- Long skewers or lollipop sticks
- Blue platter for serving
How to Make It:
1. Thread green grapes, honeydew, and kiwi alternately onto skewers.
2. Arrange on a blue oval platter in a wavy, flowing pattern.
3. Add sprigs of fresh mint between skewers for extra “seaweed” texture.
4. Label as “Seaweed Skewers” for the full themed experience.
Pro Tip: Add some cucumber rounds to the skewers – they look great and give kids a savory break from all the sweet treats.
33. Sand Dollar Cookies
Beautiful round shortbread cookies decorated to look like sand dollars are an elegant, impressive treat that guests of all ages will love – and they’re easier to make than they look.
What You’ll Need:
- Shortbread or sugar cookie dough
- Round cookie cutter
- White royal icing
- Piping bag with fine tip
- Fine white or tan edible sugar for texture
How to Make It:
1. Roll and cut dough into circles, then bake according to recipe.
2. Once cooled, flood each cookie with white royal icing and let set completely.
3. Using a fine piping tip, pipe the classic sand dollar pattern: five oval “petals” radiating from the center, plus a small star shape in the middle.
4. While still wet, dust lightly with fine white edible sugar for texture.
5. Allow to dry fully before arranging on a display platter.
Pro Tip: Watch a quick sand dollar piping tutorial on YouTube – once you see the simple pattern, it takes just seconds per cookie.
34. Clam Shell Cookies
Clam-shaped cookies with a pearlescent finish – these look stunning on a dessert table and make wonderful take-home treats that double as party favors.
What You’ll Need:
- Sugar cookie dough
- Clam shell cookie cutter
- Pink, white, and lavender royal icing
- Edible pearl dust or luster dust
- Small round candy pearl to place “inside” each clam
How to Make It:
1. Cut and bake clam-shell-shaped cookies.
2. Flood with pink or white royal icing and let set completely.
3. Once dry, use a fine brush to apply edible pearl luster dust over the entire cookie for a shimmery iridescent finish.
4. Place a small round candy or pearl sprinkle at the base of each clam to look like a pearl inside the shell.
Pro Tip: Wrap individual cookies in cellophane tied with ribbon for elegant take-home favors. Label them “A pearl of a treat!” for extra fun.
35. Starfish Nuggets
Chicken nuggets molded or cut into starfish shapes – this is the genius move that makes a simple kid-friendly food into an “oh my gosh, how did you do that?” moment at the party.
What You’ll Need:
- Ground chicken or store-bought chicken nugget mix
- Starfish cookie cutter or sharp knife
- Breadcrumbs for coating
- Oil for frying or baking sheet for oven
- Dipping sauces in ocean-themed cups
How to Make It:
1. Season ground chicken and press into a flat layer about 1/2-inch thick.
2. Use a starfish cookie cutter to cut out shapes.
3. Coat lightly in breadcrumbs.
4. Bake at 400°F for 15-18 minutes or until golden and cooked through.
5. Serve with ketchup in small ocean-themed cups.
Pro Tip: In a time crunch? Buy regular star-shaped frozen nuggets from the grocery store – they exist and they’re a life-saver!
36. Candy Sea Glass
Homemade hard candy “sea glass” in frosted blue, green, and amber colors is a gorgeous, unique treat that looks like actual sea glass found on a beach – and it’s totally edible.
What You’ll Need:
- Hard candy recipe (sugar, corn syrup, water, flavoring)
- Blue, green, and amber food coloring
- Baking sheet lined with parchment
- Powdered sugar for coating
- Small cellophane bags for display or favors
How to Make It:
1. Make a standard hard candy recipe and divide into three batches.
2. Color each batch – ocean blue, seafoam green, and amber.
3. Pour onto parchment-lined sheets and let cool completely.
4. Break into irregular “sea glass” shaped pieces.
5. Toss in powdered sugar for a frosted, sea-worn look.
Pro Tip: Display in a clear bowl or jar filled partway with white sand – it looks exactly like a bowl of real sea glass and makes a stunning tabletop decoration that guests can also eat.
37. Shark-Infested Jell-O Cups
Blue Jell-O cups with gummy sharks “swimming” inside them – these are the treat kids pick up first every single time. They’re simple, spooky-fun, and totally on theme.
What You’ll Need:
- Blue Jell-O (Berry Blue flavor)
- Clear plastic cups
- Gummy sharks
- Optional: Swedish fish or gummy fish to add variety
How to Make It:
1. Prepare Jell-O according to package directions and pour into clear cups.
2. Refrigerate until just starting to set (about 1-1.5 hours – still slightly jiggly).
3. Press gummy sharks into the Jell-O at different angles so they look like they’re swimming.
4. Return to fridge and let set completely before serving.
Pro Tip: For a “shark fin” effect, press a shark gummy in so only the fin sticks out above the surface. Kids go absolutely wild for this detail.
38. Under the Sea Popcorn Munch
Blue and teal-tinted popcorn mixed with ocean-colored candy-coated chocolates, fish crackers, and white chocolate sea shells makes the most addictive party snack mix that disappears within minutes.
What You’ll Need:
- Plain popped popcorn
- Blue and white melted candy melts
- Blue M&Ms or similar candy
- Goldfish crackers
- White chocolate shell-shaped candies or pearl sprinkles
- Edible blue glitter
How to Make It:
1. Drizzle melted blue and white candy melts over popped popcorn and toss gently to coat.
2. Spread on parchment paper to cool.
3. Once set, break apart and transfer to a large bowl.
4. Mix in M&Ms, Goldfish crackers, and chocolate shells.
5. Finish with a dusting of edible blue glitter for sparkle.
Pro Tip: Package in small cone-shaped bags tied with blue ribbon as a take-home party favor – it’s adorable and super affordable to make in bulk.
39. Ocean Blue Lemonade Popsicles
Homemade lemonade popsicles with layers of ocean blue and white – these are refreshing, beautiful, and perfect for outdoor summer parties. They also photograph incredibly well.
What You’ll Need:
- Fresh lemonade (homemade or store-bought)
- Blue food coloring or blue raspberry flavor
- Coconut milk or cream for white layer
- Popsicle molds and sticks
How to Make It:
1. Color half your lemonade blue with food coloring or use blue raspberry lemonade.
2. Pour a layer of blue lemonade into each mold (about one-third full) and freeze for 30 minutes.
3. Pour a thin layer of sweetened coconut cream on top and freeze for another 20 minutes.
4. Top off with more blue lemonade, insert sticks, and freeze completely (at least 4 hours).
Pro Tip: Add a small gummy fish or Swedish fish into the mold before adding the final layer – it’ll be a little surprise when kids bite in!
40. Sea Animal Fruit Salad
A vibrant fruit salad with star-shaped watermelon, fish-shaped honeydew, and blueberry “bubbles” is a healthy, gorgeous, and totally themed addition to your party spread.
What You’ll Need:
- Watermelon
- Honeydew melon
- Blueberries
- Strawberries
- Star, fish, and shell-shaped cookie cutters
- Fresh mint for garnish
How to Make It:
1. Slice watermelon and honeydew into 1/2-inch slabs.
2. Use cookie cutters to cut sea animal shapes – stars for starfish, ovals for fish.
3. Arrange in a large clear bowl or on a platter by color.
4. Scatter blueberries throughout as “bubbles.”
5. Add halved strawberries for coral pops of red.
6. Garnish with fresh mint sprigs to look like seaweed.
Pro Tip: Serve in a large clear bowl so the layers of color are visible – it looks like an aquarium full of sea creatures.
🎮 Under the Sea Party Activities & Games
41. Underwater Treasure Hunt
This is the activity that gets every single kid off their chair and running around the party – and it burns off energy in the best possible way. Hide “treasures” around the party space and send kids on a mission to find them all.
What You’ll Need:
- Treasure map printables (find free ones online or make a simple one yourself)
- Plastic coins, gems, or small toys as “treasure”
- A treasure chest box or decorated shoe box
- Clue cards for a multi-step hunt
How to Play:
1. Before the party, hide treasure items or clue cards around the party space.
2. Give each child or team a treasure map at the start of the activity.
3. Kids follow the map and clues to find the hidden treasure.
4. The final “treasure chest” should have a small prize for everyone – no losers here!
Pro Tip: For younger kids, keep it simple with 3-4 easy hiding spots. For older kids, write riddle-style clues that require a bit more thinking – they love the challenge!
42. Fish Mask Craft Station
Set up a craft table where kids decorate their own fish or mermaid masks – they’ll wear them for the rest of the party and take them home as the best favor ever.
What You’ll Need:
- Plain white paper masks (available in bulk on Amazon)
- Washable paint in ocean colors
- Glitter, foam stickers, and sequins
- Feathers, fabric scraps, and gems
- Craft glue and brushes
How to Set It Up:
1. Set up a craft table with all materials laid out in cups and trays.
2. Place a paper mask at each seat for kids to decorate.
3. Let kids freely paint, glitter, and decorate their own ocean creature mask.
4. Allow to dry during cake or snack time, then kids can wear them home.
Pro Tip: Have a few example masks already made to inspire kids – but don’t make them too perfect or the kids will try to copy exactly instead of getting creative!
43. Pin the Fin on the Fish
A hilarious, classic party game with an ocean twist – this is perfect for filling 15 minutes when kids need structured activity, and it works for ALL ages.
What You’ll Need:
- A large poster of a fish (DIY or purchase a themed party game set)
- Cut-out “fins” – one per player
- Tape or sticky tack on each fin
- Blindfold
How to Play:
1. Hang the large fish poster at kid height on the wall.
2. Blindfold the first player and spin them gently two times.
3. Hand them their labeled fin and point them toward the poster.
4. They stick the fin where they think it belongs – no peeking!
5. The player who places their fin closest to the correct spot wins.
Pro Tip: Make it extra funny by using hilarious labels on each fin – “Grandma’s fin,” “The birthday kid’s fin,” “The fastest swimmer” – kids love the personalization.
44. Musical Islands
This is musical chairs with an ocean twist – instead of chairs, kids “swim” to paper islands when the music stops. It’s active, hilarious, and perfect for burning off party energy.
What You’ll Need:
- Large pieces of blue and yellow construction paper or foam sheets (one per player minus one)
- A speaker for music
- Ocean or beach-themed playlist
How to Play:
1. Scatter “island” sheets on the floor – one fewer than the number of players.
2. Play music and have kids “swim” (wiggle and swim-walk) around the islands.
3. When the music stops, everyone must stand on an island.
4. The player without an island is “out” – but they become the DJ for the next round!
5. Remove one island each round. The last kid standing wins!
Pro Tip: Make eliminated kids “sea creatures” who must do a funny ocean animal impression – it keeps them engaged and entertained instead of sitting on the sidelines feeling left out.
45. Under the Sea Story Time Circle
Gather all the little ones for a calm, magical 10-minute story time in the middle of the party – it’s the perfect way to transition between activities, calm the energy, and lean into the ocean theme in a sweet, memorable way.
What You’ll Need:
- An ocean-themed children’s book (“Mermaid School,” “The Snail and the Whale,” or “Hello, World! Ocean Life”)
- A cozy spot – blankets, floor cushions, or a soft rug
- Optional: the reader can wear a simple mermaid crown or fin prop for extra fun
How to Do It:
1. Designate a cozy “story cove” area with cushions and a soft blanket.
2. Gather all the children together before cake time or as a wind-down activity.
3. Read the story with enthusiasm – do the voices, pause for questions, make it an event.
4. After the story, ask each child to share their favorite sea creature as a sweet wrap-up.
Pro Tip: Choose a book that features a diverse ocean of creatures – not just mermaids – so every child can find an animal they love and feel included in the story.
Ready to Make a Splash?
There you have it – 45 Under the Sea birthday party ideas that cover everything from showstopping décor to crowd-pleasing treats to activities that’ll keep kids entertained all afternoon.
The best part about this theme? You don’t have to do all 45. Pick the ideas that fit your budget, your time, and your little one’s personality – even just 5 or 6 of these ideas executed well will create a party your child will remember for years.
Whether you go full mermaid magic, dramatic deep-sea shark vibes, or a soft pastel ocean dream, you’ve got everything you need to pull it off beautifully.
Now go make some waves, host. Your little one’s underwater adventure awaits.
