I am making one big baby block as a cake for my nephew. The inside is going to (hopefully) be rainbow, so 6 layers. Will I need support between the top and bottom 3 layers? I'm thinking I'll make the cake 8"x8" as it only needs to feed 20... or should I make it 10"x10"?

Thanks for any advice you can give me

Id put a cake board between the 3 layers.