The best way to protect internet access is at the source. For example you can't install any of this software on an xbox or playstation. By making a couple of simple alterations to your broadband router you can gain complete control of your local internet access. Visit OpenDNS | Internet Navigation And Security for more info.
So after your kids stumble on a hardcore porn site and have image in their heads that can never be removed, you're able to discover that they visited it? Hmmm. I'd rather put my time and effort into making sure thay couldn't access sites like that in the first place!
I like ActyMac DutyWatch Remote.
ActyMac DutyWatch Remote is a complex solution for remote computer monitoring of users activities. It can record and log everything - from recording keystrokes typed and website visits, to chats, emails and screenshots. ActyMac - DutyWatch employee monitoring for Mac OS X
I definitely agree with this. I've it set up for a few families and they all love it. Its free for home use, there's a server edition for companies which costs thousands so the quality of this product is high.