Just use the standard advice on this thread.
Kids usually rie when they're ready and this can be 3, 4, 5 ,,,,etc. Just make sure that he can reach the groung easily when you've taken the pedals off. This will give him the confidence that he will be able to stop himself falling. Finding a gentle slope leading onto level ground is good as he would be able to get up a little speed which will enable him to begin to balance with his feet off the ground.
Once he can do that and change direction while balancing, he'll be ready to have his pedals back on.
Once he does that, he will, at first, probably need a helping hand, but never, ever, push the bike, which will then go where you are pushing it, which is not necessarily exactly the same direction he is steering it. A light push on his upper back will be sufficient.
One coaching mantra we always use is "look ahead, not down". The latter makes for more wobbles.