How about a toy piano, Schroeder style?

On the other hand, Schroeder, don't be to hasty. This might be Lucy some years later:   Oh, My!!

One the other hand, I have a friend (a musician) who got her two-year-old son a small Casio keyboard, showed him a couple of simple things, and he took off. He's learning to play and having a ball at it.

Don Firth