The other day I asked my youngest daughter (who just turned 6 on Sunday) to go next door and get her brother for supper. As I watched her run barefoot across our driveway and into the next yard, I was completely jealous. Her form was freaking perfect, and she streaked across the pavement like she was running in a grass field - feet landing right below her body, slight forward lean and if had closed my eyes I dont think I would have even heard her running at all - she was that smooth.
Ugh - maybe I should have her coach me
Kids have it easy in that they don't have decades of doing things wrong/reinforcing bad things. I remember going around barefoot a lot as a kid. I could run full speed on our bluestone driveway (big sharp stones too). It was just natural.
Somewhat related, I have done some work teaching folks to do squats. Kid squat naturally and do it a lot when they're playing. It's another thing adults tend to lose.
Kirk