Planning your little one’s first birthday? An Under the Sea (or Oneder the Sea) theme is perfect for creating a whimsical, colorful, and memorable celebration!
Here’s a complete guide with ideas for decor, snacks, games and activities, and party favors to make your event unforgettable.

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Invitations.
Decide whether you want to do an “under” or “oneder the sea” theme, and get your invitations to match that theme.
Other than that specific wording, there’s not a lot of difference between the two themes, other than using the word “one” more in the party in a punny way.
You can get custom invitations on Zazzle in different color schemes and with or without custom photos. Have them printed for you or download them to send digitally.
Your color scheme can be anything you want, but the most common colors for this kind of ocean theme are pink, blue, green, and purple, and sometimes iridescent pearl colors.
Click to see first birthday invitations on Zazzle.
Decor ideas.
Ocean balloon arch:
Create a stunning entrance with pink, blue, teal, and purple balloons in various shades to mimic the color theme of your party invitations.
Fishnet backdrop:
Hang a fishnet with starfish, seashells, and dangling jellyfish cutouts for a fun photo booth backdrop.
Bubble garland:
String together clear balloons to create a floating bubble effect around the party area.
Sea turtle cake topper:

This custom sea turtle cake topper can be made in different colors, and will add a special touch to the birthday cake.
Sea creature cutouts:
Decorate with cardboard cutouts of sea turtles, dolphins, and mermaids to bring the ocean to life.
Table centerpieces:
Use glass bowls filled with blue water beads and floating candles to resemble mini aquariums.
Shells on the cake table:
Scatter seashells and strands of pearls on the cake table to decorate the table in an ocean theme. Use a blue tablecloth or a paper one with printed sea creatures on it.
You can get shells on Amazon (#ad) or at the craft store.
Ocean-themed paper tableware.
Get custom paper plates, napkins and cups on Zazzle to match the name and birthday date of your guest of honor. You can get them in pink or blue to match your invitations and carry the theme through the party.

Snacks and treats.
Ocean cupcakes.
These printable cupcake wrappers from Greengate Images can be downloaded and cut out as many times as you need to create a display of ocean-themed cupcakes.
Add these cute whale cupcake toppers to finish the look!
Fish-shaped sandwiches:
Use a fish-shaped cookie cutter for sandwiches filled with kid-friendly ingredients.
Ocean jello cups:
Make blue jello cups topped with gummy fish for a fun, wiggly ocean treat.
Seashell cookies:
Decorate sugar cookies with seashell shapes and pastel icing.
Octopus hot dogs:
Cut hot dogs to resemble octopus legs and serve with dipping sauce.
Seafoam popcorn:
Sprinkle popcorn with a drizzle of light green or blue chocolate to give it a colorful twist.
Starfish rice krispie treats:
Use a starfish mold to shape Rice Krispie treats, let them cool off, then dip into chocolate and sprinkle with blue or pink sprinkles. Get silicone starfish molds on Amazon (#ad).
Games and Activities.
There are a lot of games that you’ll be able to set up for this kind of party theme. If you can have the party outside it will open up a lot of water-themed activities, too.
Treasure hunt:
Hide small seashells and plastic pearls for a treasure hunt adventure. Make the prize a small treasure chest full of chocolate coins.
Stringing seashell necklaces:
Get shells at the craft store and provide yarn and tapestry needles for guests to string the shells together to make fun necklaces.
Pin the tail on the mermaid:
A twist on the classic party game with an ocean theme.
Bubble station:
Set up a bubble machine outside and let kids play with wands and bubble guns.
Sea creature coloring station:
Provide ocean-themed coloring pages and crayons for creative fun.
Fishing pond:
Use magnetic fishing rods and fish for a safe, engaging toddler activity.
Sensory water table:
If your party is outside, fill a water table with blue-dyed water, floating sea creatures, and shells for sensory play.
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Party Favors.
You have a lot of options with an under the sea theme…If it’s summer and you live near the ocean, you can incorporate practical beach toys into the mix, too.
Mini buckets with beach toys:
Send each guest home with a small bucket, shovel, and sand molds. If your party is happening during the summer you should be able to find pre-made sets at a local store
Sea-themed stickers:

Include a sheet of stickers for the kids featuring mermaids, fish, and starfish, and give your adult guests these cool hermit crab stickers by Robert Phelps Art as something a little more upscale!
Ocean bath toys:
Rubber ducks, whales, and fish toys perfect for bath time fun.
Seashell necklaces:
Give out pre-made necklaces of strung shells, or make them as a craft activity during the party.
Bubble wands:
A perfect fit for the theme and endless fun for toddlers. See bubble wands and sets on Amazon (#ad).
Under the sea storybooks:
Small board books with ocean themes make a sweet, educational gift. There are a lot to choose from on Amazon (#ad) or get some at your local bookstore.
Make your little one’s first birthday a magical, unforgettable event with these creative Under the Sea party ideas.