R..
I taught my brother when he was 4. I took the pedals and training wheels off his bike, so he could use his legs to push and coast. That taught him his balance. Once he could coast for a while without needing his feet on the ground, I put the pedals back on and he was riding like a champ! (and he didn't have a single crash... until he got braver than his skills allowed. lol.) :)