Many years ago, my then-girlfriend Cathy and I were babysitting her friends' kids in some sleepy burg out in the boondocks, and we decided to take the kids to the local 'drome to watch the airplanes.
Lo and behold, who should we come across but a friend of mine, a CFII whose student was busy puking on the tarmac after his first simulated instrument flight. So we talked for a while, and my friend agreed to take Cathy, me, and the kids up for a ride in the 170 while his student finished losing what was left of his lunch.
The youngest child, Tony, was four years old and sat on my lap in the right seat. After takeoff, my friend asked Tony if he wanted to fly the airplane. Tony, of course, said, "Sure," and proceeded to fly the airplane. Quite well, in fact. My friend would point out landmarks, and Tony would steer toward them. He also showed him how to use the yoke and told him to maintain altitude (something like, "Make sure this needle points to the number three"), and within a few minutes, Tony was applying elevator to correct his altitude without prompting.
Tony flew the plane right up until the landing flare with not very much correction from my buddy (except, of course, for the rudder pedals, which Tony couldn't reach) and did quite a good job. What impressed me most was how quickly he understood and applied what my friend the CFII was telling him.
Cathy and I split not too long after that, and I lost touch with the family. I always wondered if Tony decided to take up flying, because he seemed to be a "natural." But my friend the CFII told me that young kids in general pick it up right away. They have a matter-of-fact outlook, and all the lights, buttons, and gauges don't seem to intimidate them.
-Rich