One of the best ways to keep track of your children when they surf the web is to sign up with a monitoring service like SafetyWeb.  For the times that you can't watch over your kids by yourself when they are surfing the Internet, this service will be invaluable.  I strongly suggest that all parents look into this subject matter, especially after the current news events of the last year where an emotionally-fragile girl was cyber-bullied by an adult woman portraying a teen-aged girl.  The girl eventually committed suicide.  What a horrible waste...I can only hope that all parents are aware of the lurking dangers of unmonitored activity by their kids on the Net.