After teaching my kids I think I know a thing or two about how to teach kids to bike. Today I saw a woman working with her 3 year old, but I saw a few mistakes. So I stopped and shared a few ideas. 

1. Never hold the bike, because it affects the child's balance. A child will never learn balance if he is removed from the balance equation.

2. Hold the child's shirt, hence you will save the child not the bike....in case the bike falls.

3. A hill is necessary! Newtonian laws of motion imply an object in motion will continue moving in the same direction. A non-moving bike will fall over, hence we need to get it moving. Gravity provides the force necessary to get the bike moving in a given direction. I used a boat ramp ( super steep hill ) to teach my kids. 

Overall, I prefer going to the top of a steep hill, hold the child's shirt, and run along side the bike. This technique can help teach a kid to bike in less than 5 minutes. I've done it.