Best kids cake icing?

[krysalyss]

I am going to build a train cake for DS' 2nd birthday from bought sponge cake.
What is the best icing for a kids party. I know what I like best - choc icing but thought it might be a bit rich for kids.
Suggestions?
Am starting to get a bit excited now!!

[Pandora]

butter cream icing, any flavour you like.
also if you are doing a cake thats shaped, if you freeze the cake it will be a lot easier to cut, as will icing with a warmed knife.