Captain Underpants Party, Including a DIY Cape and Free Printables!

Another year bites the dust! My oldest baby is officially 8. We celebrated last weekend with a Captain Underpants themed duck pin bowling party. Here’s the full party recap:


I used Publisher to make the invitations. I used a google image search to find the skyline and Captain Underpants characters, and a free “Photo CutOut” app to trim around an image of my son and saved as a new picture. I put it all together and saved it as a jpeg to text out:

Party favors:

The main party favor was Captain Underpants capes. Here were my basic steps, using a cape that E already had as a template:

  1. Trace the template onto ironed fabric and cut out 2 giant rectangles of the front (polka dot) and back (solid red) panels of fabric, with the cape pattern centered.
  2. Sew the front and back panels of fabric together with the wrong sides facing out for each fabric. Sew along the line (cape pattern), except for a 6-8 inch opening on one side.
  3. Cut excess fabric off the edges, being careful not to cut the sewed edges when cutting between each strap (leave enough space for scissors to cut between each strap while sewing around the cape pattern).
  4. Admire how pretty your cape looks so far. 😁
  5. Sew a reinforcing stitch along the end of each strap. (I added this step in after accidentally poking a hole through the end of a strap when turning the cape inside out. Learn from me – don’t skip this quick and easy step. 😉)
  6. Turn the cape inside-out by pulling it through the unstitched gap, so the right side of your fabric is visible. (A Moana oar is greatly helpful for the straps during this step, but I guess a pencil or something else could work, too. 😉)
  7. Iron the cape to help eliminate the puckered edges.
  8. Sew around the cape again (I used a reinforcing stitch for added durability) – this time, sewing around the entire edge.
  9. Pin and sew Velcro onto each strap, being careful to attach to the top of one strap and back of the opposite strap (so they will attach together when the straps lay flat).
  10. Pat yourself on the back for a job well done!

I used some new-to-me hook and loop integrated Velcro (so you don’t have to sew a hook side and a loop side), which is advertised as “snag free” Velcro. It doesn’t feel like it’s a secure hold, but for the lightweight cape it held very well. And I don’t mind the idea that it’ll separate easily enough if it gets caught on something, since it’s worn around the neck… Here’s an action shot of our boys to show how well the Velcro holds up:

We also had goodie bags. The bowling alley had some gift certificates for each kid to include, but we added silly “potty putty” (thanks, Target Dollar Spot!!), whoopee cushions (Party City was cheaper than Amazon), stickers, and little DIY comic/ coloring books (what would a Captain Underpants party be without books?!).

Coloring/ Comic Book_Free Printable.pdf

Any Captain Underpants fan will appreciate the make your own “Flip-o-Rama”! It also included a guide to your Villian name and Professor Poopy Pants name (obviously, haha).

I reused the invitation publisher file to create a party bag label.

Thank You Bag Label_Free Printable.pdf


You know I was most excited about decorating the cake!! Thanks to the Baking Championship shows on the Food Network, I had enough confidence to try making a cake with fruit filling (if kids can do it, I can, right? No. Poor assumption 😂). Turns out, I very much needed my husband to talk me through this and help me with the structural supports (his mom is a professional cake baker and decorator, so he actually knows his stuff). It was touch-and-go for a while!!

Okay, here was my process (and where I think my rookie mistakes were):

  1. I leveled each cake, then surrounded the edge of each bottom cake with frosting. But I used whipped cream frosting throughout (probably should have used something with more structure for between the layers, like buttercream or cream cheese frosting?).
  2. I poked holes in each bottom cake to cram as much fruit filling in as possible (also could’ve messed with the structure, but I don’t regret this step).
  3. Topped with the fruit, then put on each top cake. Although it’s not visible, I had a cardboard circle under the bottom of each layer (each layer being 2 cakes with the filling in the center).
  4. Added more frosting to start a crumb coat (yea, I totally guessed here because I am only pretending that I know what I’m doing).
  5. Added a sugar glaze over each layer. This step was REALLY helpful when frosting to help eliminate crumbs. I let this dry/harden for at least an hour before frosting.
  6. Mixed 4 shades of blue for my frosting, and frosted in an ombré pattern.
  7. Not pictured: I put 4 wooden skewers into the bottom layer to support the top cake layer, then transferred the top layer (and touched up the frosting).
  8. Cut a city skyline out of modeling chocolate (I dyed it black first). I loved these tools for working with the modeling chocolate. I found it as easy to work with as fondant, but trickier to transfer to the cake (because it would stretch almost too easily).
  9. Made a modeling chocolate “8” and pair of underwear. Used the modeling chocolate tools to sculpt groves and fill in with edible marker.
  10. Panicked that the top layer was falling apart (the top cake was sliding off the bottom cake). My husband reassured me that this was no big deal, and carefully pushed the top cake back into place with a spatula, while I pushed skewers all the way through both layers. I had to go slow and twist (to get through the cardboard at the bottom of the top layer), but it worked really well. The picture above was taken while pushing the 3rd or 4th skewer into place.
  11. Made a toilet paper roll out of modeling chocolate, using an edible marker to write Happy Birthday E on it, and a fork to puncture perforated edges. I put it on the cake, but waited on the underwear until we got to the bowling alley (I didn’t want it to slide down the cake since it seemed heavy).
  12. Next I worked on the cake topper, using an image as inspiration. I don’t have a ton of pictures of this step because I was really in the groove. Just imagine this step starting with 8 pre-made Rice Krispie treats crammed together into a compact rectangle (two layers of 4 treats). This gave me enough for the body (including the arms), and I used a few more around the edges to help add to the cape. I wanted 2 layers to make it easier to cut the body shape out, while leaving a single layer for the cape around the legs.
  13. This is where I gave up because I knew the Rice Krispie treats would be way too heavy to stand upright on the (already structurally fragile) cake. Again, my husband gave me the rational solution: use supports! Duh!!! So I stuck 4 skewers through the head, and ended up using 2 toothpicks in each arm and a couple more around the cape edges.
  14. I slowly cut away to form the body and cape shapes, and the sculpting tools were critical in this step.
  15. Once I had the basic shape, I started covering each section with dyed modeling chocolate, using the sculpting tools and a gloved hand to smooth it out as I went (THIS is a great use for modeling chocolate in comparison to fondant – I liked it more than when I used fondant over the wings of the Toy Story cake). I made the ears, mouth, nose, eyes, eyebrows, and polka dots all separately before transferring to the face and cape. Eyebrows are tricky – took me a while to get them shaped to look happy instead of angry, haha!
  16. I also made the cape tie separately before adding, and that piece was what finally made him look like Captain Underpants to me. I put the whole thing in the freezer for a few hours before we left for the party, and put it on the cake at the bowling alley. But I took some pictures of everything before we left (just in case it something didn’t make it in one piece to the party)! The talking potty was a birthday gift for E that seemed right to include on the cake platter.

I also made a backup paper topper in case something went wrong during transfer or assembly…

Spoiler alert: although the top layer started to split on the drive to the alley, I was able to fix it with frosting when we arrived, so it all made it!

I stuck 2 toothpicks under the underwear to make sure it wouldn’t slide down the cake. Here’s the moment of truth (and a picture of the finished goodie bags!)…

I extended the modeling chocolate down the support skewers, which was helpful to allow the cape to appear more like it was in the air.

The birthday boy approved of the cake!

By the way, his T-shirt was made using a personalized, downloadable file I purchased from this Etsy shop. I used iron-on transfer paper and followed the package instructions to print and transfer the image to a t-shirt. Quick and easy!

And of course I had to get more pictures after he had his cape on (and with his souvenir bowling pin)!

And duckpin bowling was fun for all the kids!

As were the video game demos… haha!

The bowling alley supplied pizza, chicken tenders, and fries, but instead I’ll share more pictures of the cake…

And our youngest boy demonstrated how delicious Captain Underpants tasted (which btw – Rice Krispie treats wrapped in modeling chocolate IS delicious)…

And the baby girl helped herself to the ice cream toppings…

Thanks to all of E’s friends that were able to celebrate with us – he had a GREAT day!!! ☺️

Now our younger son has been talking about requests for HIS next birthday! He’s requesting a “real” Captain America shield. I kind of hope he still wants a Marvel theme by August; a super hero cake sounds fun (and my head is already spinning with ideas)! ☺️

4 thoughts on “Captain Underpants Party, Including a DIY Cape and Free Printables!

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