Under the Sea Birthday Party

We threw an Under the Sea Birthday Party for my 3 year old, complete with a Mermaid Cake and Oyster Pearl Cookies. All of the food and decorations fit in with this beach ocean themed party.

Charlotte is 3 sign on a fishing net filled with balloons for an Under the Sea Birthday Party

For my youngest’s 3rd birthday, we hosted an outdoor Under the Sea Birthday Party. I’ll take you through the planning, decorations, food, and desserts. I’ve included lots of ideas for a fun and festive ocean themed party!

under the sea birthday party food table

Mermaid Under the Sea Party

Because we were having an outdoor pool party for Charlotte’s 3rd Birthday, I encouraged her to choose a Mermaid Themed Party / Under the Sea Themed Party. She loved the idea!

I made her a shirt to wear on her actual birthday, which was a week before the party. Her shirt says “This little mermaid is 3.” I found some pretty holographic heat transfer vinyl at a local vinyl store and also a mermaid patterned vinyl that I used for the 3. I cut the vinyl using my Silhouette machine.

This Little Mermaid is 3 t shirt and build a bear

On her actual birthday, we took her out to lunch and to Build A Bear for their “pay your age” Bear. Because we got a good deal on the bear, we let her choose an outfit. You can see how nicely the bear matches her!

I also made my two older girls t-shirts to wear that day that say “Mermaid squad.” I designed them so the “A” in “Mermaid” is a starfish and the end of the “d” in squad has a mermaid tail. I used the same holographic vinyl as for Charlotte’s shirt.

Mermaid Squad t shirt

Under the Sea Birthday Party Decorations

While Charlotte’s cake was Mermaid themed, I decided to go with an Under the Sea Birthday Party theme to give more options for decorating and fitting the food into the theme. I got so many of the ideas for this party from Pinterest. I will try my best to give credit to the source when possible!

DIY Fish Net Balloon Decoration

In designing the food table, the main focus was this fish net party decoration to hold balloons over the food table. It was a very windy day, which was quite frustrating when trying to assemble this focal point. Balloons kept blowing away and the lettering for “Charlotte is 3” kept blowing in all directions. It took more time than I had budgeted to get this assembled, but I have a few tips, as well as a suggestion I wish I had known about at the time.

under the sea birthday party balloons in a fish net

I wanted pearlized balloons rather than typical matte ones to add some shine. In fitting with the color scheme, I chose white, purple, and seafoam colored balloons. We blew them up all around the same size. I’ve seen some where you blow some up large, some medium, and some small, which is also very cute.

To hang the fish net, I used clear fishing line to suspend the net from some nails under our deck. You could try using outdoor command hooks if you don’t already have an easy place to tie to the fishing net. I tied it up on each end and in the middle. Then, I folded the net up half way and started securing the sides together with clear fishing line. The spacing is important because you don’t want a balloon to be able to fit through and blow away.

Once a little pocket was created, I started tying up the top with fishing line to create a closed pocket, but I left enough space on one end to add the balloons. I added the balloons inside the net, then moved them over to fill it. Once full, I tied up the remaining section. At this point, it may be necessary to go back around all of the edges to make sure there’s not a hole for the balloons to escape. When the wind blows the net, it really puts pressure on the balloons and they can get out easily if the edges aren’t tied.

Balloon Garland

After this party, I attended a birthday party for my cousin’s son and discovered balloon garland strips. It’s a clear strip with little holes in it that is used to secure a bunch of balloons together for a balloon garland. This would have been much easier! If I had to do it over, I would first secure all the balloons to the strip, then place the garland into the net and then tie it in just a few places to secure the balloons. This would have prevented rogue balloons from escaping the net!


For the “Charlotte is 3” lettering, I cut individual letters of champagne glitter cardstock with my Silhouette machine. I then used a needle and fishing line (rather than thread) to poke through places on the cardstock so I could tie the letters to the fishing line. This was a bit tedious, but with the wind, it was necessary to secure each letter. Some of the letters could be tucked into the net.

Jellyfish Decorations

I didn’t get a good picture of the “jellyfish” decorations I made. They were just mint / seafoam colored paper lanterns with strips of disposable table cloths cut up and tied onto the bottom of the lantern. Like I said, the wind was out of control, so these were blowing in the breeze, as you can see in front of Charlotte.

jelly fish decorations blowing in the breeze at an Under the Sea birthday party

Under the Sea Centerpieces

As I’ve mentioned in my posts on Ava’s FROZEN Birthday Party and Cinderella Birthday Party, I like to use disposable tablecloths to decorate at parties. Not only are they a super inexpensive way to add color to the party, they make clean up so easy.

under the sea birthday party themed table in front of a swimming pool

This table originally had a disposable table cloth on it, but the wind was blowing it up and knocking over the centerpieces, so we finally decided to ditch the table cloth. I used another fish net party decoration as a table runner and added some glass gems / glass vase fillers to weight it down.

I filled small metal flower pots from IKEA with tissue paper and glass gems and then stuck a wooden dowel rod in the center. The wooden dowels were covered in crepe paper and wrapped in jute twine. I then attached mermaid and seahorse silhouettes I cut out of glitter cardstock with my Silhouette.

under the sea birthday party themed table centerpieces on an outdoor table

Another centerpiece I used was small plastic bowls filled with crushed graham crackers and the fondant beach shapes I made for the Mermaid Cake.

bowl with fondant shells and seahorses in crushed graham crackers to look like sand

Mermaid Art

To make this Mermaid “3” art, I used a circular craft punch to punch out purple, mint, and champagne glitter cardstock. I cut the “3” using my Silhouette and really pretty holographic, textured cardstock I found at a local craft store. I glued the circles onto a piece of 5×7-inch white cardstock to look like mermaid scales and then placed the 3 on top. I used an IKEA frame I already had that has a clear, plastic front instead of glass, as avoiding glass is ideal around a pool.

mermaid scales made with cardstock with a 3 on top inside a picture frame

Nautical Rolled Napkins

Another Pinterest find! I purchased 3 colors of paper napkins and rolled them around plastic cutlery: a fork, a knife, and a spoon inside each napkin. I then tied them with jute twine in a fancy little knot and added a mint lifesaver candy. One tip about these candies: they are very minty. I recommend unwrapping them and letting them sit out for a few days before you need them to dampen the mint smell. I didn’t want the napkins to smell too much like mint.

bowl of cutlery wrapped in paper napkins tied with hemp twine with a white mint lifesaver attached

During my many shopping trips while planning this party, I found this tumbler that matched the theme perfectly. This was a little gift to myself.

sparkly blue wine tumbler on a table filled with ice water

Ocean Themed Party Food

I wanted most of the food to fit the Under the Sea Party theme. I made the food labels with brown Kraft cardstock and a white paint pen. Adhesive rhinestones added a little bit of sparkle to the food labels.

Pool Snacks

We always serve snack by the pool to tide guests (and our kids!) over until dinner. The “seaweed dip” was Costco spinach artichoke dip, La Terra Fina brand. Tortilla chips and carrot stick “crab legs” were for dipping.

bowls of spinach artichoke dip, carrot sticks, and tostitos scoops

This container of pretzel sticks was labeled with “drift wood” and tied on using jute twine and a mint lifesaver.

container of pretzel sticks next to napkins and bowl of fishie crackers

My kids LOVE goldfish crackers, both the classic cheese ones and the pretzel goldfish. I found this little plastic candy scoop at Party City to serve with a bowl of both kinds of “fishie crackers.”

bowl of cheese and pretzel goldfish with plastic scoop
table with disposable plates and cups and snacks
food table with a decorated mermaid picture frame and snacks

My kids are big fruit lovers, so no pool party would be complete without a fruit platter.

fruit platter on a table

Lunch or Dinner

under the sea birthday party food table
under the sea birthday party food table

I kept it very simple and ordered a tray of Costco croissant sandwiches. They come as a variety of 3 sandwiches: ham and cheese, turkey and cheese, and roast beef and cheese. The tray also comes with a mustard mayo spread and a basil mayo spread. We’ve used these sandwich trays for birthdays and Baptisms when I’ve been too busy to make all of the food and desserts myself.

platter of Costco croissant sandwiches with googly eyes on toothpicks stuck in each

To make these “crab wiches,” I used hot glue to adhere googly eyes onto toothpicks. I assembled all of the googly eye toothpicks in advance and then placed them into the sandwiches to look like crabs before serving the sandwiches.

When she turned 3, Charlotte was super picky. She was even in occupational therapy for eating issues! I knew she wouldn’t even try one of the croissant sandwiches. One of her favorite foods at the time was Uncrustables, and because of the shape and crimped edges, I called these “clam wiches.”

smuckers uncrustables on a food table

We had salad with homemade croutons and chips, but none of these had themed labels.

food table with salad, croutons and chips

These dill pickles were “sea cucumbers.”

bowl of dill pickles with label "sea cucumbers"

These green grapes on wooden kabob skewers were labeled “seaweed.”

green grapes on wooden skewers labeled "seaweed"

We made multiple boxes of Velveeta Shells n Cheese and labeled them “shells & cheese.”

glass dish of velveeta shells and cheese labeled "shells & cheese"

This jello was another Pinterest find. It’s called “sea glass” (or “beach glass”) and has different layers.

container of jello cups labeled "sea glass"

It’s basically just blue and purple jello, each divided into two portions. One was left plain and the other has whipped topping (Cool Whip) folded in to make it opaque. The jello was then all layered into disposable clear cocktail cups so each guest could just grab one from the buffet.

cup of jello to show the 4 layers

See all of the layers!

4 layers of jello on a plastic spoon

Oyster Pearl Cookies

clear serving platter with Oyster Shell Cookies on top

I saw this idea on Pinterest and thought they were SO cute, I just had to make them. We didn’t really need another dessert to go with the Mermaid Ice Cream Cake, but I usually like to offer an alternative.

These cookies are easy for guests to grab, just like a Bar dessert, so they can be offered as a sweet treat before the main birthday cake is served. All the details for making the cookies are in the post Oyster Pearl Cookies.

Oyster Pearl Cookies
Adorable Oyster Pearl Cookies fit any Under the Sea or Ocean Themed Party. Delicious Easy Vanilla Buttercream piped onto Nilla Wafers with a pretty shimmer chocolate Sixlets candy pearl inside.
Check out this recipe
seashell cookies / oyster shell cookies

I did not serve these at the party, but these painted Starfish Cookies would have been super cute with this theme!

Starfish Cookies
These easy Starfish Cookies are made by painting iced shortbread or sugar cookies. Use a simple egg free icing for no piping! Works with royal icing as well.
Check out this recipe
Starfish Cookies on a plate

Mermaid Birthday Cake

My girls are big fans of my Dairy Queen Copycat Homemade Ice Cream Cakes. One of my favorite things about ice cream cakes, aside from the fact that they taste AMAZING, is that the top is a literal blank canvas for decorating.

Charlotte really wanted an ice cream cake, so I decided to decorate the top to fit the theme of Mermaids and Under the Sea. All the details of how to decorate the cake and make the ocean themed fondant decorations are in my Mermaid Birthday Ice Cream Cake post.

Mermaid Birthday Cake on a table by a pool
Mermaid Ice Cream Birthday Cake
A Mermaid Ice Cream Birthday Cake with fondant mermaid tails and edible seashells, starfish, and seahorses. Perfect for a mermaid, beach, or ocean themed birthday party!
Check out this recipe
Mermaid Birthday Ice Cream Cake

Our Little Mermaid certainly had a great birthday!

birthday gift with a card that says "happy birthday princess" with the little mermaid on it

Summary of Under the Sea Birthday Party Sources

I purchased many of my supplies locally but will list some online sources as well for convenience.

Holographic HTV
Silhouette Portrait
Fish net party decoration
Clear fishing line
Balloon Garland Strips (I did not use but wish I would have!)
Pearlized balloons
Glass gems vase filler
Circular craft punch
Glitter cardstock
Brown Kraft cardstock
Adhesive rhinestones
White paint pen
Googly eyes and toothpicks
Hot glue gun
Plastic scoop
Disposable table cloths
Paper lanterns
Mint lifesavers
Jute twine

Under the Sea Dessert Recipes

Oyster Pearl Cookies
Starfish Cookies
Mermaid Ice Cream Birthday Cake

Under the Sea Birthday Party Pin

Looking for More Birthday Party Ideas?

Check out these other Parties I’ve thrown for my girls:
Daniel Tiger Birthday Cake and Party
Very Hungry Caterpillar Birthday Party
Sesame Street Birthday Party
My Little Pony Rainbow Unicorn Ice Cream Cake
FROZEN Birthday Cake and Party
Cinderella Birthday Cake and Party
Tea Party Ideas for Kids
Penelope Bird Birthday Party
Winter Wonderland Birthday Party

These Rainbow Brownie Ice Cream Sandwiches and Painted Rainbow Cookies were just for fun but would be perfect for a Rainbow Birthday Party!

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