31 Magical Under the Sea Birthday Party Ideas & Decorations

11/02/2025Last Updated: 11/02/2025

Dive into a world of wonder with an Under the Sea birthday party! Whether you’re planning a 1st birthday for a boy or girl or a fun-filled celebration for older kids, this magical theme brings the ocean to life. With shimmering blue decor, sea creature-inspired treats, and exciting underwater-themed games, your party will make waves with guests of all ages.

From DIY Under the Sea decorations to creative Under the Sea birthday party food, there are endless ways to transform your space into an underwater paradise. Think jellyfish lanterns, mermaid tails, pirate treasures, and ocean-inspired desserts that are both delicious and Instagram-worthy.

Under the Sea Birthday Party Ideas

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Whether you’re planning an Under the Sea birthday theme for a girl with mermaids and pearls or an Under the Sea birthday theme for a boy featuring sharks and submarines, there’s something for everyone.

In this guide, we’ll explore the best Under the Sea party ideas, including DIY decorations, exciting Under the Sea birthday party games, and creative Under the Sea food ideas that will make your celebration truly unforgettable!

Under the Sea Birthday Party Invitations

Setting the tone for your Under the Sea birthday party starts with the perfect invitation! Whether you want something elegant, playful, or adventurous, these Under the Sea birthday party invitations will excite your guests and make them eager to dive into the celebration.

1. Message in a Bottle Invitations

Give your guests an exciting start to their Under the Sea party with a message in a bottle invitation! Simply roll up the invite like an old-fashioned scroll, place it inside a small glass or plastic bottle, and add tiny seashells, sand, or small pearls for a realistic touch. You can tie the bottle with twine and attach a mini tag that says, “Open for a magical undersea adventure!” These invitations are perfect for a 1st birthday or older kids and can be customized with mermaid or pirate-themed elements.

2. Mermaid-Themed Invitations

For a girl’s Under the Sea birthday party, create mermaid-themed invitations that shimmer like the ocean! Use pastel colors like seafoam green, lavender, and pink, and add elements like mermaid tails, pearls, and glittery scales. You can also attach a mini starfish charm or use holographic paper for a magical effect. These invitations can be in the shape of a mermaid tail, seashell, or even a treasure chest for a unique touch.

3. Shark Attack Invitations

For a boy’s Under the Sea birthday theme, make the invitations exciting with a Shark Attack design! Create a bite-shaped invitation where the edges look like a shark has taken a big chomp out of the card. Use bold blue colors with shark fin silhouettes and fun phrases like, “You’re invited to an epic Shark Adventure!” or “Swim fast to [Child’s Name]’s birthday party!” These invitations are perfect for kids who love ocean creatures and action-packed themes.

4. Underwater Pop-Up Cards

Take your invitations to the next level with Underwater Pop-Up Cards! These 3D invitations open up to reveal colorful sea creatures, coral reefs, and bubbles, making the invite feel like an immersive underwater scene. You can DIY these pop-up cards using craft paper and stickers or order custom ones online. Whether you choose a playful dolphin, a magical mermaid, or a pirate’s treasure chest popping out, these invitations will leave a lasting impression on your guests.

5. Bonus Tip: Digital Animated Invites

If you prefer digital invites, create animated Under the Sea invitations with swimming fish, rolling waves, and glittery text using e-card websites. This is an eco-friendly and interactive way to invite guests while keeping the theme alive!

These Under the Sea birthday party invitations will set the perfect mood for an oceanic celebration, making guests excited to join in the fun! 🌊🐠✨

DIY Under the Sea Decorations

Transform your party space into a magical underwater world with these DIY Under the Sea decorations! From shimmering jellyfish to floating bubbles, these simple yet creative ideas will bring the ocean theme to life for your Under the Sea birthday party.

6. Jellyfish Lanterns

Create enchanting jellyfish lanterns using paper lanterns and flowing streamers to make it feel like they’re floating in the deep sea. Here’s how to make them:

Use pastel or iridescent paper lanterns in shades of blue, purple, pink, and white.

Cut long strips of crepe paper or ribbon in matching colors to create tentacles.
Attach the streamers to the bottom of the lantern using tape or glue.
Hang the lanterns from the ceiling at different heights to give the illusion of jellyfish swimming around the room.
These decorations add movement and an elegant touch to your Under the Sea birthday party decorations.

7. Bubble Balloon Wall

Mimic the look of floating bubbles with a bubble balloon wall! This backdrop is perfect for a photo area or behind the food table.

Use a mix of clear, white, and light blue balloons to create the bubble effect.
Inflate them in different sizes and attach them to the wall in clusters.

For an extra touch, add small LED lights inside some of the balloons to make them glow like real bubbles!
This simple DIY idea makes a big impact and enhances the underwater theme of your party.

8. Fish Netting with Seashells

Give your space a beachy feel with fish netting draped with seashells. This is an easy decoration that can be used on tables, walls, or even as a photo booth backdrop.

Use store-bought fishnet or make your own by cutting string into a crisscross pattern.

Attach seashells, starfish, and mini sea creature toys to the net using glue or clear fishing wire.
Hang the net along the walls, over tables, or on chairs to complete the nautical vibe.

9. Underwater Table Setting

Make your party table feel like it’s submerged under the sea with an underwater table setting:

Use blue tablecloths as the ocean base.
Sprinkle faux pearls, starfish, and coral pieces across the table.
Use seashells as name card holders or mini bowls for candy.
Place mini treasure chests or glass bowls filled with blue water and floating candles as centerpieces.
This table setup adds elegance to your Under the Sea party, whether for a girl’s mermaid theme or a boy’s pirate adventure.

10. Hanging Paper Fish & Seaweed

Give your party space an immersive ocean feel by hanging paper fish and streamers that look like seaweed.

Cut out colorful fish shapes from construction paper or print out templates.
String them up using fishing wire and hang them from the ceiling.

Create seaweed by twisting green crepe paper streamers and letting them hang down like underwater plants.
Add glitter or iridescent paper for extra shimmer to make it look like sunlight filtering through the water.

These DIY Under the Sea decorations will make your birthday celebration truly magical and transport your guests to an underwater wonderland! 🌊🐠✨

Under the Sea Birthday Party Games

No Under the Sea birthday party is complete without fun and exciting games! These interactive activities will keep kids entertained while staying true to the ocean theme. Whether you’re hosting a mermaid-themed party for a girl or a shark adventure for a boy, these Under the Sea birthday party games will make a splash with your guests!

11. Treasure Hunt 🏴‍☠️🌊

Turn your party into an underwater treasure hunt by hiding “sunken treasure” around the party area.
How to play:

Hide golden coins, pearls, or small treasure chests filled with candy or prizes.

Create a simple treasure map or give kids clues to find the hidden items.
Add fun obstacles like “swimming through the seaweed” (streamers) or “diving under coral” (chairs or tunnels).
The child who finds the most treasure wins a special prize!
This game works well for both 1st birthday parties and older kids who love adventure.

12. Pin the Tail on the Mermaid 🧜‍♀️

A classic party game with an underwater twist!
How to play:

Draw or print a large mermaid poster without her tail.
Cut out mermaid tails from colorful paper.
Blindfold each player, spin them around, and let them try to pin the tail in the right place.

The player who gets the tail closest to the correct spot wins!
For a boy’s birthday theme, swap the mermaid for a Pin the Fin on the Shark version.

13. Shark Attack Tag 🦈🏃

This high-energy game is perfect for active kids!
How to play:

Choose one player to be the “shark” while the rest are “fish.”

The fish run around, trying to avoid being tagged by the shark.
When tagged, a player must freeze in place until another fish “rescues” them by tapping their hand.
The game continues until all fish are caught, then a new shark is chosen.
This game is great for outdoor Under the Sea birthday parties!

14. Underwater Ring Toss 🎯🐙

Test your guests’ aim with a sea-themed ring toss.
How to play:

Set up an inflatable octopus, shark, or sea creature with upright tentacles or fins.
Have kids take turns tossing rings onto the tentacles.
Each successful toss earns points, and the player with the highest score wins!
This game is easy to set up and can be adjusted for different age groups.

15. Fishing for Prizes 🎣✨

A fun and interactive game where kids “fish” for goodies!
How to play:

Fill a small inflatable pool or bucket with blue tissue paper (to mimic water).
Attach small prizes (stickers, toys, or candy) to paper fish with paper clips.

Give each child a toy fishing rod with a magnet or clothespin at the end.
Let them take turns fishing and collecting their prizes!
For an Under the Sea 1st birthday party, make it easier by allowing toddlers to scoop up prizes with a small net.

These Under the Sea birthday party games will keep your little sea explorers entertained and engaged throughout the party! 🌊🐠💙

Under the Sea Birthday Party Food 🌊🐠🍴

Make your Under the Sea birthday party even more magical with these ocean-inspired treats! Whether you’re hosting a mermaid-themed birthday for a girl or a shark-themed party for a boy, these creative Under the Sea food ideas will delight kids and adults alike.

16. Mermaid Tail Cupcakes 🧜‍♀️🧁

Turn regular cupcakes into a mermaid’s dream with glittery tail toppers!
How to make:

Bake cupcakes in ocean-colored wrappers (blue, teal, or purple).
Frost them with swirls of pastel buttercream.
Add edible glitter or shimmer dust for an extra magical touch.

Top with candy or fondant mermaid tails.
These elegant cupcakes will be the highlight of any Under the Sea birthday party!

17. Octopus Hot Dogs 🐙🌭

A fun and easy snack that kids will love!
How to make:

Cut the bottom half of a hot dog into 6-8 thin strips to create “tentacles.”

Boil or pan-fry the hot dog until the tentacles curl up.
Place them on a plate with a dab of mustard or ketchup for eyes.
Perfect for a boy’s Under the Sea birthday theme, especially if he loves sea creatures!

18. Seashell Sandwiches 🥪🐚

Transform simple sandwiches into ocean treasures!
How to make:

Use a seashell-shaped cookie cutter to cut out sandwich bread.

Fill with kid-friendly ingredients like peanut butter & jelly, ham & cheese, or cream cheese & cucumber.
Arrange on a platter with pearl-like grapes or round mozzarella balls for a cute touch.
A great option for Under the Sea 1st birthday parties, since they’re soft and easy to eat!

19. Ocean Jelly Cups 🐟🍮

A wobbly, fun treat that looks like the ocean!
How to make:

Prepare blue gelatin in clear cups.
Before it fully sets, add gummy fish or sea creature candies inside.
Let them chill until firm, then top with whipped cream “waves” and sprinkles.
Serve with mini spoons for an easy grab-and-go snack.
These cups are a fun and colorful addition to your Under the Sea birthday party food table!

20. Seaweed Popcorn 🍿🌿

A simple yet creative snack that looks like real seaweed!
How to make:

Pop plain popcorn and toss it with melted white chocolate.
Mix in a few drops of green food coloring and stir until coated.

Let it dry, then serve in ocean-themed cups or bowls.
This snack is a great way to add a savory-sweet twist to your Under the Sea food menu!

With these fun and delicious Under the Sea birthday party food ideas, your guests will feel like they’re dining under the ocean! 🌊🐠💙

Under the Sea Birthday Party Decorations 🌊🐠✨

Transform your party space into an enchanting underwater world with these stunning DIY Under the Sea decorations! Whether you’re planning a mermaid-themed birthday for a girl or a shark-inspired celebration for a boy, these ideas will bring the ocean theme to life.

21. Shimmering Blue Drapes 🌊🎭

Create a breathtaking underwater illusion using sheer blue fabric!
How to set it up:

Hang layers of blue and teal fabric from the ceiling or walls.
Use soft LED lights behind the fabric to create a glowing ocean effect.

Add a few iridescent or glittery streamers for a magical touch.
This decoration instantly transforms any room into a deep-sea adventure!

22. Giant Clamshell Seat 🐚📸

A show-stopping photo booth idea that makes guests feel like sea royalty!
How to make it:

Cut and paint large foam boards into a clam shape.

Add pearlescent paint for a shimmering effect.
Use cushions or a bean bag inside to create a cozy “throne” for the birthday star.
This works beautifully for Under the Sea 1st birthday parties or a mermaid-themed celebration!

23. Starfish & Coral Centerpieces 🌟🪸

Dress up your tables with ocean-inspired decor!
How to create them:

Arrange real or artificial starfish, seashells, and coral pieces on each table.

Use sand-filled glass jars with tealight candles for an elegant glow.
Add pearls or mini treasure chests for a fun pirate or mermaid touch.
These centerpieces bring a beachy vibe to your Under the Sea birthday party decorations!

24. DIY Sandcastle Display 🏰⛱️

A magical Under the Sea decoration that doubles as a party attraction!
How to make it:

Build a realistic sandcastle using sand, glue, and cardboard boxes.
Display it as a table centerpiece or a party entrance prop.
Add tiny seashells, mermaids, or pirate figures for extra detail.
This idea is perfect for both boys and girls who love ocean adventures!

25. Bubble Machine 🫧🐬

Nothing says “Under the Sea” like floating bubbles!
How to use it:

Set up a bubble machine near the party entrance for a grand ocean-like welcome.
Use glow-in-the-dark or LED-lit bubbles for a magical “deep-sea” effect.

Let kids chase and pop bubbles for a fun, interactive element!
A bubble-filled atmosphere makes the party feel like a real underwater adventure!

These DIY Under the Sea decorations will transport your guests to an ocean wonderland, making the party a magical and unforgettable experience! 🌊🐠✨

Under the Sea Birthday Party Favors 🎁🐠🌊

Send your guests home with ocean-inspired party favors that keep the magic of the Under the Sea birthday party alive! From mermaid-themed keepsakes to treasure chest surprises, these favors are perfect for kids of all ages.

26. Mini Treasure Chests 💎🪙

Give each guest a tiny treasure chest filled with ocean treasures!
What to include:

Gold chocolate coins
Candy pearls
Mini seashells
A small toy or trinket
These chests fit perfectly with a pirate, mermaid, or sea explorer theme!

27. Mermaid Tail Keychains 🧜‍♀️✨

A sparkly and fun favor for mermaid lovers!
Why they’re great:

Cute, colorful, and practical
Available in glittery, pastel, or metallic designs
A lasting keepsake kids can clip onto their backpacks
Perfect for a girl’s Under the Sea birthday party!

28. Shark Tooth Necklaces 🦈📿

A cool and adventurous favor for kids who love sea creatures!
Why they’re popular:

Great for a shark or ocean explorer theme
Can be real (faux shark teeth work too!)
Kids will love wearing them as a fun accessory
A hit for boys’ Under the Sea birthday parties or anyone who loves sharks!

29. Sea Creature Plush Toys 🐬🐙🐳

Give each guest a mini ocean animal plushie!
Options include:

Dolphins
Octopuses
Whales
Starfish
These adorable plushies make a perfect Under the Sea 1st birthday favor for little guests!

30. Ocean-Themed Sticker Books 🏝️🎨

A fun and creative takeaway gift!
Why kids love them:

Interactive and engaging
Filled with sea creatures, mermaids, and pirates
Keeps kids entertained even after the party
Great for both boys and girls who love Under the Sea adventures!

31. Personalized Seashells 🐚🖋️

A unique and special keepsake for guests!
How to make them:

Collect or buy smooth seashells.
Write each guest’s name using a metallic or glitter pen.
Add small decorations like pearls or tiny starfish.
These DIY Under the Sea party favors are a simple yet memorable way to thank guests for coming!

With these Under the Sea birthday party favors, your guests will take home a piece of the ocean and remember the fun long after the party ends! 🌊🐠🎁

More Birthday Party Ideas:

58 Minnie Mouse Birthday Party Ideas for the Perfect Celebration

Final Thoughts,

An Under the Sea birthday party is a magical and exciting way to celebrate a special day. Whether it’s a 1st birthday for a boy or girl or a themed event for older kids, this oceanic adventure is full of fun, creativity, and imagination. With DIY Under the Sea decorations, delicious Under the Sea food ideas, and engaging Under the Sea birthday party games, your party will be a splash!

From shimmering jellyfish and seashell treats to treasure hunts and mermaid magic, this theme offers endless possibilities for an unforgettable celebration. Now that you have all the inspiration you need, it’s time to start planning and bring the Under the Sea party to life! So, grab your seashells, set up your underwater paradise, and let the fun begin! 🌊🐠✨

11/02/2025Last Updated: 11/02/2025