The short answer? They're people with connections.

It doesn't matter how smart you are: you don't work in a university lab at age 11 without someone pulling strings for you. (Unless they're counting stuff like gifted/talented summer camps as "work".)

You occasionally see high school kids in the lab in summer doing some sort of trivial research. The best cases are disadvantaged kids who have access to science advocacy programs. The worst cases are kids whose parents have influence and/or work at the university. It's one of the things that drives me nuts about dog-and-pony shows like the Intel science fair -- smart kids who don't have access via ambitious/overzealous parents don't have a chance.