- Start with a bike small enough that the seat can be set to allow feet flat or nearly flat on the ground while seated.
- Remove the pedals and training wheels. (One pedal will be reverse-threaded, turning backwards)
- Let them ride until they are balancing. For a kid in the summer, anywhere from a few days to a few weeks. They will probably start with very little coasting between foot pushes. Eventually there will be long periods of coasting between pushes, this means they are ready.
- Put the pedals back, or move to the bigger bike.
That's all there is to it! This is easiest when a child is fairly young, and won't feel silly without pedals. An excellent time to do this is when a child has outgrown their current bike and is ready for the next size--both my kids did this when outgrowing the smallest size sidewalk bike.
Both my kids did this when they went from 12 inch wheels to 16 inch.
If you aren't going to be using the outgrown bike again, it will be slightly easier for the kid if you remove the crank and chain as well as the pedals.