That's one of the reasons I installed W2K on the kids machines. They access the internet through my machine, so my wife and I have complete control over when they are on line. I use a proggy called Proxy from AnalogX for logging and the kids know I check it regularly. If I see where one of them went some place they shouldn't, I disable their password. If they don't turn it off or don't do their homework when told, I either use VNC to shut them down or I disable their password. It's worked very well so far.
Harder