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!What about keylogger i prefer use KeyBag.I use it on my Mac to monitor the websites that visited by my children,It helps me a lot.
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.In my opinion K9 web protection is one of the best free product for web content filter for kids (and even some adults!)
see -> K9 Web Protection - Free Internet Filtering and Parental Controls Software
For more general info look around Internet Safety & Security Issues look at Parental Control | Home too.
Hope this helps