If you don't have filtering on your computers put it on. #5's molester started with pornography and decided he had to try it out.
Please put some filtering software on your computers. DH likes open dns. It blocks things at the router so all the computers that use the same router have filtering. (At least that is how I understand it to work. There are lots of filtering packages out there.)
And IF you don't know how to get filtering software, regularly check the history and put passwords on the computer.