I have a tip when making Birthday cakes for very little ones. Instead of saying "What would you like for your Birthday cake darling?" instead use a statement like "How would you like an 'x' Birthday cake?" where 'x' is something that you want to or can easily make. I'm not sure up to what age you can get away with this, but it certainly worked very well with Harry, and he was thrilled with his Button Moon cake. In terms of cakes, you really can't get much simpler. A plain Victoria sandwich cake with yellow butter icing and four chocolate buttons in the centre!