Unfortunately the parental controlls on most software is fraught with problems...many of them are'nt (were'nt) smart enough to seperate real from fake dangers...for example if they want information on breast cancer most software will (would) screen it out as a hazard...
the best parental controll your friend can have on his computer is himself...
consider passwording the internet window, and have him monitor their activities...I have used the present/past tence because it has been several years since I had them set up on my PC (and subsiquently removed them) they may have improved the filters by now....but I'm also sure those sites wishing to be seen have also improved their methods also...
I have found the best monitoring I can do is to disallow any chat/IM/ membership and restrict the use for legitimate research and have a frank discussion as to the dangers and pitfalls (as well as the good)...
there is no reason for kids to be surfing the web, chatting with their "friends"...
put down the PS2/gamecube/gameboy/PC/ TV and go out side and ...play...use your imagination...be a kid...if you need to talk to your friends...pick up the phone and call them....
Password the entire internet connection...is the best safe gaurd, and honest communication with your kids!
