I planned an Under the Sea Little Mermaid–themed birthday party for my daughter’s 3rd birthday, and I’m sharing the exact decorations, food ideas, party favors, and Amazon finds we used.

When my daughter was getting ready to turn 3, there was absolutely no question about the theme — she is obsessed with Ariel. From singing “Under the Sea” on repeat to pretending she’s a mermaid in the bathtub, she lives for all things ocean and princess magic. I wanted to create an Under the Sea Little Mermaid birthday party that felt special, colorful, and fun… without being overwhelming. This party came together with a mix of simple DIYs, Amazon finds, and a few easy touches that made the day feel truly magical for a 3-year-old who believes she’s part mermaid.

This party is from my second daughter’s 3rd birthday, but fun fact—I used this exact theme for my oldest daughter’s 3rd birthday too.

I’ll walk you through this setup first, then you can scroll down to see how I created a similar look for her party as well.

That first party was in our previous home, which had a smaller space—and honestly, it made the decorations feel even more full and immersive. Everything felt closer together, which really brought that “under the sea” look to life.

Disclosure

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An Under the Sea Ceiling That Brought the Party to Life

To bring the theme to life, I completely turned the living room (this party was at my Mom’s house) into an underwater ocean. I hung blue tablecloths across the ceiling to create a deep-sea feel, then cut out fish and whales from cardstock paper and scattered them throughout the room. The transformation was honestly better than I expected — it felt colorful, immersive, and magical without being complicated. To really sell the “under the sea” vibe, I hung a giant whale float (I used this one) from the ceiling along with jellyfish decorations from Amazon, and it ended up being everyone’s favorite part of the room. I hung these with fishing line so they truly looked like they were floating. Everything is linked for you below the photos!

Ocean decor we used:

• Blue Plastic Table Cloth
• Construction Paper for Fish/Sea Life silhouettes (I free handed these drawings but you can also trace them onto computer paper from your computer screen and then cut them out and trace them onto the construction paper)
• Whale Pool Float Toy (I used this one)
• White Bubble Garland (I used these) and hung them from the ceiling
• Jellyfish decor (we used these) to hang from ceiling

Of course we had to have a balloon arch! 🎈 I’ve made so many at this point that I’ve gotten surprisingly fast at putting them together. I originally taught myself using a great “how-to” video (linked here) on YouTube, and now I can bust one out in no time. Balloon arches are one of those decorations that look impressive but are actually very doable once you’ve made one or two. I honestly couldn’t find the exact balloon arch kit I used since it was a couple years ago but I found another great Under The Sea colored one that I would totally use if I were doing another party with this theme!

• Under the Sea Balloon Arch Kit (linked here)
• Ariel backdrop sign (couldn’t find the exact one I used but I honestly found a better one and linked it for you)
• Mermaid Table Cloth

Mermaid Inflatable Cooler (I used this one)

Dinglehopper Cake Pops (Made by Dad!

One of the biggest hits at the party was the “dinglehopper” cake pops my husband made. 🧁 Inspired by The Little Mermaid, he added small forks into each cake pop to turn them into Ariel-approved dinglehoppers, and the kids absolutely loved them. They fit the Under the Sea theme perfectly and were just as popular with parents as they were with the kids. It made the moment even sweeter knowing they were homemade by Daddy — such a simple touch that ended up being incredibly special.

• Cake Pop Recipe (linked here)
• Silver Plastic Forks/Dinglehoppers
• Purple Wafer Melts (for dipping the cake pops into for color)

Ariel’s Grotto: The Kids’ Favorite Activity!

One of the biggest crowd-pleasers was the bouncy house we set up in our downstairs family room. We added a sign that said “Ariel’s Grotto,” which made it feel extra special and totally on theme. The kids were obsessed and spent so much time bouncing and playing. We used this exact bouncy house from Amazon, and it worked perfectly for all the different age groups at the party.

Inflatable Bouncy House (this one)

Ariel coloring books souvenirs for the kids (Amazon doesn’t carry these anymore but THESE ones are too cute

Mermaid Wine Labels (a big hit with the parents)

Another Under the Sea Party Using the Same Decorations

When I say I loved this theme… I really mean it.

This wasn’t actually the first time I created an under-the-sea birthday party like this. I originally used these same decorations for my oldest daughter’s 3rd birthday—and it turned out just as magical.

What I loved most was how versatile everything was. The jellyfish lanterns, the balloon garland, the ocean table setup… it all came together in a slightly different way but still created that same underwater feel.

For her party, I leaned into:

• Hanging jellyfish decorations across the whole room
• A mix of pastel and bright ocean colors
• A fun ocean-themed food table with cupcakes and a matching cake
• Floating balloons and even a giant whale overhead (which the kids were obsessed with)

It ended up feeling like you were walking into a little underwater world right in our living room.

I’m so glad I reused these decorations because it made planning so much easier the second time around—and honestly, I think it looked just as special.

If you’re wondering whether you can reuse party decor for multiple kids or parties… the answer is absolutely yes. With just a few small changes, it can feel brand new every time.

I’ve included a few photos from her party below for more inspiration!

• Whale Pool Float Toy
• Jellyfish decor
• Mermaid Balloon Arch Kit
• Little mermaid inflatable toddler pool (ours is no longer available but this one I found is so similar!)

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Real Mom Party Prep Tip:
Honestly, the biggest part of getting ready for this party wasn’t the decor… it was cleaning my house 😅

I always do a full reset before hosting, and a few things make it SO much easier (especially with kids running around).

Shop my go-to cleaning favorites below:

2 in 1 Shark Matrix Robot Vacuum and Mop: My 2-in-1 sark vacuum mop robot vacuum is honestly a life saver- I just let this thing run while I’m party prepping and it makes such a difference.

Tineco Cordless Vacuum Mop: I also love my Tineco mop that vacuums and mops at the same time-with 3 kids and a puppy, I feel like I constantly need both!

Shop this Party

Decorations

• Blue Plastic Table Cloth
• Construction Paper for Fish/Sea Life silhouettes (I free handed these drawings but you can also trace them onto computer paper from your computer screen and then cut them out and trace them onto the construction paper)
• Whale Pool Float Toy (I used this one)
• White Bubble Garland (I used these) and hung them from the ceiling
• Jellyfish decor (we used these) to hang from ceiling
• Under the Sea Balloon Arch Kit (linked here)
• Ariel backdrop sign (couldn’t find the exact one I used but I honestly found a better one and linked it for you)
• Mermaid Table Cloth
• Mermaid Inflatable Cooler (I used this one)

Homemade Cake and Cake Pops

• Cake Pop Recipe (linked here)
• Silver Plastic Forks/Dinglehoppers
• Purple Wafer Melts (for dipping the cake pops into for color)

Activities for Kids

• Inflatable Bouncy House (We love this one because it can be used for little kids and kids a little bigger with the slide feature)
• Ariel coloring books souvenirs for the kids (Amazon doesn’t carry the exact ones we used anymore but THESE ones are too cute!)

The perfect finishing touch to the party was surprising our birthday girl with a special visit from a real-life Princess Ariel, along with face painting for all the kids. Watching her eyes light up was one of those moments I’ll never forget. The kids were completely in awe, the parents loved it just as much, and the entire party felt truly magical from start to finish. Even months later, my daughter still talks about “when Ariel came to her party,” which tells me everything — it was a day full of joy, imagination, and memories we’ll always treasure.