I found that the problem seems to be with parental controls. I wasn't told when the problem actually started, and I'm sure he was fooling around with something...
Anyways, if you go into their account, go to System Preferences, click on Accounts. Unlock the padlock, and click on the account you want to correct. Click on Open Parental Controls at the bottom, and click on the Content tab. Where it says to limit access, click Customize. In the top box, you can type in the websites that will be ok to access.
This has worked for us, however, it still doesn't resolve why the problem came up in the first place. So, I'll leave it unresolved, and see if anyone comes up with the fix.
Hope this helps...
Mark.