Good way to learn is to get a bicycle (borrow maybe?), remove pedals and cruise to build up confidence. Lower the seat, start at a flat ground and just push yourself (as kids do). Then you can move on a slight downhill to gain some speed and learn to operate the brakes. Once that becomes easy you can move onto pedaling.. which is cycling!
You should see my three-year-old on his coaster bike. I can no longer keep up with him, even running. I haven't transitioned him to pedals yet, but I have to feel there's something to the idea that the balance is the hard part and once you're confident in that you can pedal while you do it.
Edit: He became proficient with it slightly after his second birthday. He walked fairly late, too, after 16 months or so. I don't think he could have learned to pedal this early, but he's got the balance, steering, and speed control (braking and accelerating as needed) out of the way. Even knows how to ring a bell when passing people on jogging trails.
