My kids are 3(boy) and 4 (girl) and I'm itching to get bikes for them. My question is how young is old enuff? Can't decide if I should start out with mini quads of bikes with training wheels. Just saw the KTM 50 mini adventure and the dealer, looks like a nice bike. Wife wants to start them out with those battery powered cars but that wouldn't be as much fun for me. What do you think?