I'm not 100% sure of this, but I'm pretty sure families on that show are paid for participation.  I do wonder about what that kind of publicity does to kids in the long run, though.  Even in their communities at the time of airing -- you're so bad you needed to be on Supernanny -- that kind of thing.

I haven't watched in a long while, since we don't normally watch Network TV, but now I'm curious about it again.  What day is it usually on?