Wow....

If they know how to re-install windows, don't bother.

Like manip said, they are 15, what sites shouldnt they be seeing... They've most probably done way 'worse' than what they could be seeing on the 'bad' sites anyway.

Anyway if the kids know whats good and bad (been taught their moralls) you don't have anything to worry about.

And everything else that manip said.