Yeah, my little nephew (2 and a half) loves trains, some of his first words were Ropley and Alresford - the local preserved line stations!
And the best thing is, when he pretends to be a steam train, he's learned (from his dad I think) to do it properly, with his arms as reciprocating con rods, instead of going round at the same time...
We got our old lego out at Xmas, and when we asked him what he wanted us to build, it was 'steam train!' over and over - we ran out of wheels!