My Little Pony was the requested theme for my daughter's 4th birthday party. I made a three-layer 9" round cake in rainbow colors. Sadly, I wasn't able to get a photo of the inside, but it was super bright and vibrant.
I got my kid-at-heart husband a cotton candy machine for Christmas, so he whipped up the blue cotton candy for the clouds. I thought it turned out as a really cool touch. I'll admit that I had much grander plans for this cake, but after a party with a dozen friends, I just wasn't up for it. The rainbow ended up laying on the cake instead of standing up, and the pony was just a toy.
Even though I wasn't able to do all the things with this cake that I had planned, it was still a huge hit with the kids and really tasty!