I've heard of the push bike thing, and it seemed like a good idea, but haven't tried it with kids.
You could also try a tandem or trailer bike, just to get the kid used to riding, pedaling, and balance (without steering).
My nephew had a tough time learning. He decided the best place to learn to ride was on Mom's (his grandmother's) front lawn. Watered, green, and soft. It has the advantage of being soft for falling, but harder to pedal (and slower which is a problem).
One issue that I had was setting the seat like I would on a road bike. Make sure the seat is set low enough that the kid can get both feet on the ground.
It is always interesting to see a kid learn. It is like a light bulb that gets switched from crashing to riding EVERYWHERE.