Can anybody give me any ideas how I can make a christening cake jointly for a 6 month old and a 6 year old? Both boys.

I,m just stuck on how to incorporate the two without over complicating things.

I have seen loads of lovely cakes with trains and blocks which would be fine but think it might look a bit babyish for the older child. Or maybe not. What do you think?

I would be grateful for any ideas. The lady only wants a one tier cake which makes it a bit more difficult for me :S