20 Under the Sea Birthday Party Ideas for Kids & Adults
Planning a birthday celebration that feels magical, fun, and unforgettable? An Under the Sea birthday party is the perfect theme to make waves of excitement for kids and adults alike!
From shimmering ocean décor and seashell-inspired treats to mermaid magic and adventurous pirate vibes, this theme transports everyone straight into an underwater wonderland.
Whether you’re hosting a cozy gathering at home or a big bash at a venue, the “Under the Sea” party theme offers endless creativity in decorations, games, food, and activities.
In this article, we’ll explore the best ideas to help you create a birthday experience that’s as vibrant and enchanting as life beneath the ocean’s surface.
1. Ocean of Wonders Backdrop
An amazing under the sea birthday party starts with a captivating backdrop. This vibrant scene offers an explosion of color, drawing guests into an aquatic adventure.
Shimmering streamers create a beautiful effect, mimicking sunlight dancing on the water’s surface. Delightful balloon arches frame the display, in soft blues, yellows, and purples.
Beloved baby shark characters and friendly starfish peek out. This charming setup is a fantastic way to welcome everyone to a memorable underwater celebration.
2. Seaside Celebration Scene
This under the sea birthday party setup brings ocean charm outdoors. Gentle waves and a friendly whale create a calming, natural feel. A surfboard adds a fun, beachy touch.
Beautiful blue and white balloons form an arch, with a seahorse and an octopus joining the fun. A custom cake takes center stage, ready for little ones to enjoy.
Coral and starfish decorations complete this enchanting display. It is truly a remarkable scene, blending marine life with coastal vibes for an unforgettable celebration.
3. Mermaid Lagoon
Welcome to a whimsical mermaid under the sea birthday party! The stunning arch and shimmering backdrop set the stage for an unforgettable day. Delicate balloons float around the display.
A custom cake stands tall on a scale-patterned pedestal. On the side, a treat stand holds colorful jars of sweets and favors, creating a stunning visual treat for guests.
The decorative mermaid tail and seashell add charm to the scene. This party idea is simply charming.
4. Playful Ocean Friends
This under the sea birthday party features an amazing, giant orange octopus made of balloons. It oversees a vibrant dessert table. Confetti balloons add a festive touch.
The backdrop showcases colorful fish and an “under the sea” setting. A delightful cake sits among various sweets and treats. Guests will adore these fun details.
A cute crab and starfish decorations complete the scene. This celebration is sure to make a splash with all the little ocean adventurers and their families.
5. Little Mermaid Magic
This beautiful display brings mermaid magic to life. A cutout of Ariel stands alongside a beautiful backdrop. Balloons in soft pastels create a magical feel.
Large starfish and seashell cutouts complete the look. The scene features three pedestals with scale and shell patterns, great for holding a cake or other treats.
This theme creates a truly enchanting under the sea birthday party setting. It is a stunning way to bring a fairytale to life.
6. Ocean Blue Celebration
This under the sea birthday party is a serene blue oasis. A custom sign welcomes everyone to “Hudson is One.” Beautiful blue and green balloons create a stunning arch.
A charming cake sits atop a fishnet-draped pedestal. Coral decorations add depth and texture. Guests will love the thoughtfully arranged table settings.
Each blue plate holds a beautifully decorated cookie. Playful fish toys complete the cheerful, inviting atmosphere. This celebration is a breath of fresh, ocean air.
7. Sweet Sea Treats
This under the sea birthday party dessert table features a whimsical octopus cake. The cake is the star of this sweet display. Playful sea creatures sit on each layer.
Surrounding the cake are adorable cookies shaped like crabs, fish, and starfish. Cake pops with tiny sea creatures are ready for guests to enjoy.
This is a fun and tasty way to celebrate. The dessert table offers an array of delightful treats, ensuring every guest finds something special to savor.
8. Magical Party Favors
Send guests home with a special memento of the under the sea birthday party! These clear gable boxes are the perfect size for holding small toys or sweet treats.
Each one features a custom name tag and a fun mermaid tail. The clear boxes showcase the delightful sea-themed decorations.
A happy octopus, a cute turtle, and colorful coral and seashells add to the charm. This is a wonderful way to thank guests and end the celebration on a high note.
9. Finding Dory Adventure
This under the sea birthday party is a whimsical adventure, taking guests on a journey with beloved characters from a popular animated film. A beautiful balloon arch in various shades of blue and turquoise creates an underwater feel.
The custom-designed birthday cake features a friendly octopus and other marine life. The table is set with playful partyware and decorations. Each place setting has plates, napkins, and cups with a themed design.
Bubble balloons and plastic sea creatures are scattered across the table. This celebration captures the joy of the movie. It is a wonderful way to bring a favorite story to life for a child’s birthday.
10. Magical Mermaid Photo Op
This stunning setup is a magical photo opportunity for an under the sea birthday party. An inflatable shell chair is the main attraction, ready for the guest of honor.
Soft pastel balloons in various sizes create a beautiful arch. It is adorned with a mermaid tail, starfish, and jellyfish cutouts. It’s a whimsical backdrop for photos.
A display stand filled with favors adds another layer of fun. It is a stunning visual display. This setup is a beautiful way to create lasting memories.
11. The Grand Sea Cake
This stunning cake is a centerpiece for any under the sea birthday party. It has four tiers of ocean-themed magic. A friendly whale and delicate jellyfish decorate the top.
The middle tier, with a clear design, shows off an adorable octopus and colorful fish. The bottom tier features sculpted coral, shells, and starfish.
It is a beautiful and detailed work of art. This cake is an absolute showstopper, ensuring every celebration ends on a sweet and spectacular note.
12. A Grand Ocean Display
This stunning under the sea birthday party setup is truly grand. Two amazing balloon octopus creations frame the central backdrop. They add a fun, whimsical touch to the display.
The scene features multiple pedestals for cakes and treats. A beautiful backdrop of an underwater scene creates a sense of depth. Cutouts of playful sea creatures add to the fun.
The glowing neon light around the base adds a modern touch. This celebration is a visual feast, ensuring an amazing time for all the little ocean adventurers.
13. Mermaid and Octopus Fun
This beautiful under the sea birthday party setup combines mermaids and an octopus. An iridescent sequin backdrop creates a shimmering effect, like light on the water.
Pastel balloon garlands and custom cutouts of a mermaid tail and sea creatures add a charming touch. The decorative pedestals are styled with fishnets and starfish.
A smiling octopus cutout and other happy sea creatures greet guests. This scene is a truly whimsical and memorable way to celebrate.
14. Delightful Ocean Cookies
These gorgeous cookies are a sweet addition to any under the sea birthday party. They are decorated in soft pastels and feature whimsical sea creatures.
The treats are shaped like smiling dolphins, friendly sharks, and cute seahorses. Some cookies are even personalized with the name and age of the birthday child.
Starfish and seashell cookies add to the ocean theme. These delightful sweets are a delicious and charming way to celebrate a special day.
15. A Playful Octopus Cake
This adorable cake is a highlight for an under the sea birthday party. A cheerful red octopus with big, friendly eyes sits on top. A small turtle and starfish join it.
The bottom layer of the cake is decorated with edible seaweed, starfish, and an anchor. A number two and the name Andrés are written on the cake.
The cake stand holds a few more ocean-themed decorations. This cake is a sweet centerpiece that every guest will remember.
16. Mermaid Lagoon Backdrop
This amazing under the sea birthday party backdrop has a pastel color scheme. The mermaid theme shines through with an iridescent sequin wall that shimmers like light on the water.
A large, custom-made seashell cutout with a name on it stands out. An inflatable mermaid tail and a pearl strand balloon garland complete the whimsical feel.
This setup is great for photos. It is a stunning visual display and a lovely way to celebrate. It is sure to be a party everyone will remember.
17. Sweet Seaside Table
This charming under the sea birthday party setup is outdoors. A ruffled pink tablecloth covers a table filled with delightful treats. A sea life banner adds to the theme.
A pastel ombre cake sits next to matching cupcakes. A custom sign with a seahorse and a number one balloon complete the sweet display.
Balloons in soft shades of pink, white, and purple sit at the base. This is a beautiful way to celebrate a special first birthday.
18. A Mermaid’s Dream Table
This under the sea birthday party table is a magical display of sweet treats. A cute mermaid is printed on the front, greeting guests. A beautiful watercolor backdrop adds a dreamy feel.
The dessert table is filled with matching cupcakes, cakepops, and other sweets. Everything is perfectly coordinated with the theme. A small cake sits on its stand in the middle.
A vibrant balloon arch with purple and pink balloons sits in the corner. This setup creates a colorful and inviting atmosphere for a fun celebration.
19. Whimsical Ocean Creatures
This whimsical under the sea birthday party setup is all about friendly ocean friends. A custom backdrop features a sweet whale, turtle, and seahorse. It is a stunning visual.
The sides of the display are decorated with smiling cutouts of a crab, octopus, and starfish. A beautiful balloon arch in soft pastels mimics ocean bubbles.
This delightful party theme creates a truly magical and memorable experience. It’s a fantastic way to welcome guests to an underwater world of fun.
20. The Grand Octopus Entrance
This spectacular under the sea birthday party features a massive octopus balloon centerpiece. It hangs from a tree, creating a whimsical and grand entrance. Its long, twisting tentacles are made of pink and blue balloons.
A simple table is set with flowers and party favors. Clear pink chairs allow the beautiful table settings to stand out. It is a stunning, eye-catching decoration.
This playful and creative theme is an unforgettable way to celebrate. The balloon octopus is a fantastic and memorable focal point. It truly brings the party to life.
