My 7 & 5 YO just learned to ride at the classes run by thte National Park service. it was awesome. I actually think a class is great for this reason - parents teaching kids to ride a bike and drive a car causes so much tension. My kids responded so much better to Ranger Jan and Ranger Eric telling them they could do it.
It sounds like it's mostly about confidence.
Here's the link to the National Park Service class with a description of the techniques they tought and a few you tube videos that show the technique.
http://www.nps.gov/gwmp/planyourvisit/learntoride.htm
http://www.youtube.com/watch?v=pRk1xZbahf0
http://www.youtube.com/watch?v=pqgCxgd3l2g
Remove pedals, lower seat so feet are flat on the ground.
The three gliding techniques were as follows:
Lizard – sit on bicycle, walking with feet on the ground
Bunny hop – use both feet at the same time to propel the bike forward
Eagle - three bunny hops, then lift feet and coast
Once child is confident in balancing, add pedals, raise seat a little higher so only the balls of the feet are touching the ground, teach “power pedal” position (pedal positioned just over the top of the arch for maximum benefit when starting off), teach braking technique and let them try.