This is a lot of conversation looking for a solution for a problem that does not exist. Let me see if I have this correctly. If I turn the handle to far, the engine goes too fast and goes off the track. Well, welcome to the fun of a 'first' train set. Based on my childhood, here are a couple of other non problems. Give him a second engine so they can be connected tender to tender and see which one can pull the other around the track. Also, make them smokers so that he can fill the room with smoke as they both are going balls to the wall. Finally there is the favorite scene of both starting at opposite ends of a long straight track wondering what will happen if the handle is kicked all the way to 'warp'.
Everyone who did not do one of these as a kid can reply.
