Teaching a child to push off My four year old started riding a pedal bike a few days ago, and thanks to his balance bike took to it like a fish to water; he's going up and down the street or park like a pro already.  

He sometimes is able to push off to start, particularly downhill of course, but on straightaways he gets frustrated sometimes.  I've taught him to adjust the pedals to the optimal starting spot (about 1 or 2 o'clock position, right?) and to try to get a little speed with his off foot, but sometimes it's just too hard.  He's used to the balance bike, and can get plenty of speed there, but just doesn't seem to 'get it' with the regular bike.  

If it's relevant, he's on a 16"/40cm wheel bike with the seat in the lowest position, and is about 44"/110cm tall; the balance bike he used was a 12"/30cm wheel bike with the seat at the highest position.  When he's on the seat his feet reach the ground, but I'm not sure if they get completely flat to the ground.

Is there a proper way to teach a young child to push off?  Anything I can do to help him other than just letting him keep trying?  He's fairly persistent fortunately, so 'keep trying' is entirely reasonable, but if there's a better technique to teach I'd love to get him started right.
In my experience, kids don't realise that they have to push hard at the start. 

It seems obvious (even "intuitive") to us, but not to them.

On the balance bike, one can just push along gently, but this new bike is bigger and heavier, and the gearing makes it harder.

So my advice is to encourage him with an enthusiastic "push hard" call. Or go further and tell him to stand on the pedal.

I solved this problem in a different way: I built my son's bike with a gear cluster at the back (no derailleur) with the chain on the easiest gear. As he got stronger, I gradually moved the chain across one cog at a time.

The main thing is to have fun with them.