DIY Little Mermaid Costumes for Siblings

This DIY Little Mermaid Costumes tutorial for siblings includes directions to make DIY Sebastian the crab costumes and a DIY Flounder the fish costume to go along with an Ariel costume.

After searching for ideas for our Halloween costumes for groups of three siblings I came upon the Little Mermaid costume. The Little Mermaid is a favorite of my girls so I thought they could each be one of the many characters.

While there are only three different costumes talked about in this tutorial, you can also add in Ursula, King Tritan, or Prince Eric costumes as well if doing this costume theme for families.

Sebastian the crab and flounder costumes are hard to find in stores because they aren’t the main characters in the movie. Because of this, we store-bought our Ariel and created this DIY to help you make your own Sebastian and Flounder costumes.

For these costumes, you can purchase all of the materials needed through Amazon or your typical local craft store (we purchased from Hobby Lobby). Scroll on to read more on how to make Little Mermaid costumes for a group of siblings.

This post may contain affiliate links and as an Amazon Associate and a member of other affiliate programs, I may earn a small compensation from qualifying purchases. All opinions and recommendations are my own.

Tips for Success

* This family costume tutorial shows a Sebastion the crab costume for babies. If making this costume for toddlers or children you can make it with a red t-shirt (or sweatshirt) and sweatpants instead of a onesie/one-piece infant outfit.

*For this Flounder costume we purchased a yellow baby shark costume that was super inexpensive (it was $10 when we purchased it). We used this as a base for our Flounder costume. You could also use a yellow onesie (one piece outfit) for an infant or yellow sweatshirts, sweatpants, and a beanie hat as the base for a children’s flounder costume.

We chose to purchase a knock off little mermaid costume to cut down on the cost instead of purchasing a real Little Mermaid costume. This was less expensive. We chose to buy our own mermaid costume instead of making one because we found it to be easy to find. We made our Flounder and Sebastian costumes because we couldn’t find them in stores.

See below for our favorite option for a Little Mermaid costume:

DIY Little Mermaid Costumes for Siblings

DIY Sebastian the Crab Costume 

For this costume, you will need a red onesie outfit or red pants and shirt, red pipe cleaners, wire, red felt, cardboard, a red beanie hat (the tighter fitting the better), hot glue gun, and white and black felt.

1. Using your hot glue gun, glue three pipe cleaners spread an inch apart to the back of your baby outfit on the left side. Repeat this process on the right side to make the smaller legs of the crab.
2. Glue longer pieces of wire (each about 6″ in length) to each of the shoulders of the baby outfit. Twirl two pipe cleaners around these until it covers them in length.
3. Cut out two pac man shaped pieces (a circle with a triangle cut out of the middle) about 3″ in diameter from a piece of sturdy cardboard. Glue and cut out red felt pieces onto both sides of each cardboard circle.
4. Glue the felt-covered circles to the wire pipe cleaners attached to each of the shoulders to make the crab’s front pinchers.
5. Cut two smaller pieces of wire (about 3″ long). Cover these with black pipe cleaners. Hot glue each of these to the top of the back of the beanie hat for the start of the crab’s eyes. You may need to hot glue a good amount of the wire piece to ensure it stands up straight when it is on the baby’s head.
6. Cut out two large circles from cardboard (about 3″ in diameter again). Glue white felt to each side of these cardboard circles. Glue a smaller black felt circle near the bottom of each white felt circle for the insides of the eyes.
7. Glue these to the black pipe cleaner covered wires coming off of the head.

DIY Flounder the Fish Costume 

If you use this yellow baby shark costume like we did it doesn’t really count as DIY because you still have to purchase a costume. However, you can than use this costume as either a baby shark or a flounder costume once finished. We did it this way because I felt it looked more like a flounder costume but you can also use a yellow outfit onesie.

*We had to make our own DIY flounder costume because while looking for a flounder costume to go with our planned little mermaid sibling costume theme we couldn’t find one in stores. Since then the movie has become big again with the remake and you may be able to find one in stores.

For this costume, you will need a yellow outfit or onesie (or a yellow baby shark costume), a hot glue gun, a scissors, two different shades of blue felt, white felt, & black felt. 

1. If using a yellow onesie cut out a large white circle from one piece of felt and glue it to the front of the onesie (if using one with a zipper, you will need to cut it in half and glue one side of each circle to each side of the zipper so it still zips up and down). *Bypass this step if using the baby shark costume

2. Cut out two long skinny light blue triangles (about 6″ long a piece) and glue one to each of the arms for the flippers.

4. Cut out two skinny blue triangles that are still somewhat long but shorter than the light blue triangles (about 4″ long). Glue them next to the slight blue triangles on the arms to complete the flippers.

5. Cut out a shape with three light blue triangles connected at the bottom. Cut out two of these shapes. Hot glue the tops of the triangles together and open them up and glue each bottom to the top of the yellow hat or hood of your sweatshirt/outfit for the head fin.

6. Cut out two large dark blue rectangles for the head and glue them together at the top . Again open the bottom up and glue each side to the hood of the outfit. Glue them right behind the light blue fin.

7. Behind the dark blue rectangles glue two smaller skinnier rectangles in light blue. 

8. Repeat this process with two more dark blue rectangles and then two more light blue rectangles to complete flounders large top fin.     *The reason for doing two separate pieces and gluing them together is to make the fins stand up straight.

9. Cut out three long skinny pieces of dark blue felt with triangular ends. (about 10″ in diameter). Glue them to the middle of the back of the hooded onesie or shark costume for Flounder’s stripes (if using the shark costume you will need to cut the middle one in the middle and glue to both sides of the top fin).

10. Cut out a trapezoid shape with rounded corners from light blue felt for Flounder’s tail. Add two stripes of dark blue felt on top going the length of the tail. Hot glue the tail to the bottom of the shark outfit or near the butt of the onesie outfit.

11. If using a hooded sweatshirt/onesie outfit you will need to cut out two small black felt circles and glue them to the top of the hood near the front for the eyes. Glue two small white felt circles on top of the blacks to finish the eyes. If using the costume you don’t need to do this.

12. If using the costume, finish by hot gluing the teeth down to the inside of the hood as Flounder doesn’t have teeth like a shark would.

We love all things Halloween including dressing up in fun family costumes each year. For another fun sibling costume idea be sure to check out this fun Bluey costume DIY Tutorial.