L was three, nearly four, when he learned to ride a bike. He was impossibly tiny, but he set his mind to it, and by day three he had figured it out (except that he had to crash to stop since his feet couldn't reach the ground.)
Whim and I immediately "got involved" to get him a bike more his size. We pulled out M's rusty old toddler-sized two-wheeler and kitted it out with new tires, and figured we were all set for some family rides.
But he could never get the hang of it again. The spell was broken. We'd pull it out every now and then, but it was useless. He didn't know how to ride anymore. We didn't push it, because who pushes a three-year-old to ride a bike? But the old saying, "It's just like riding a bike." Why couldn't he remember?
Today, struck by the thought that he is now five and it is definitely time, I showed him a video of himself riding that day long ago. Remember? You used to know how. Want to try again?
And then it dawned on me. Instead of the little old bike, I let him ride the big bike again- the same bike he learned on- and he rode down the street and back again, just like that.
Umm... The little bike didn't work?! Why did it take me a year and a half to think of that?!
This afternoon, we rode to the pool to celebrate. I planned to run alongside him, but he rode all the way there without a hitch. (Though on the way back he faceplanted into a fence!)