Where they get these kids, I don't know. I did catch an episode -don't know if it was SUper or Nanny911-where the son said in front of the camera that his mother told him he could be as bad as he wanted to be that day. I think there is perfomance involved for some, but the rest are just naughty little bugs.
I think they should show updates on the families after longer time has passed. Just a week after the show isn't time to tell if things are really on the right path or not.