Rainbow Double Birthday Cake

This cake was MASSIVE!! I was asked to create a double birthday cake for my niece and nephew who had just turned 1! I was told something simple... Well as you can tell i don't really know what SIMPLE is. I got slightly stuck when coming  up with an idea because i needed something that would work for both genders. Thats when Tiffany came up with the idea of doing a Rainbow cake and here is the result!