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.

If you love ocean-themed parties, don’t miss my first under the sea birthday party post for even more decorations, food ideas, and inspiration.

Disclosure

This post may contain Amazon affiliate links, which means I may earn a small commission at no extra cost to you if you make a purchase through my links. I only share products I truly love and use. As an Amazon Associate I earn from qualifying purchases.

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)

The Party Planning System I Use for Every Party

Planning a birthday party?

After years of planning themed birthday parties for my own family, I finally turned my party planning system into a printable guide you can use too.

Plan Your Next Kid’s Party Without the Stress

Planning a themed birthday party has a lot of moving parts, and it is so easy to forget the little things (like cake servers or lighter matches!). To keep myself completely sane while putting this Gabby party together, I used my signature 16-Page Printable Party Planning System. It tracks everything from your budget and guest count to a strict ‘Party Day’ timeline. You can grab the exact system I use on Etsy below for just $4.99 to make your next party totally stress-free!

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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)

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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!

More Under the Sea Birthday Inspiration

This wasn’t actually our first Under the Sea birthday party — we loved this theme so much that we recreated it years later for our second daughter’s 3rd birthday too. Both parties had a completely different look and feel, and it’s so fun to look back on them side by side. You can check out our first ocean-themed celebration here for even more inspiration!

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 Birthday Party Planning System I Use for Every Party

After years of planning birthday parties for my family, I finally turned my party planning system into a printable guide that helps keep everything organized in one place.

My 13-page Birthday Party Planner walks you through the entire planning process, from two months before the party all the way through party day. It includes planning timelines, guest lists, gift tracking, cleaning checklists, party-day reminders, and space for notes throughout the planner.

Whether you’re planning a simple family celebration or an elaborate themed party, this planner is designed to help you stay organized and enjoy the celebration process a little more.

👉 Grab My 13-Page Birthday Party Planner Here

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.