I think a lot of things are self-taught by nine-year-olds: the basics of engineering (I know a nine year old who built a potato gun!), sports, arts and crafts,

I think a lot of things are self-taught by nine-year-olds: the basics of engineering (I know a nine year old who built a potato gun!), sports, arts and crafts, networking, animal care, and these are just the things off the top of my head :)