I think an application to control/monitor access on the internet would be usefull. Something that could resctrict access to certain websites, allow/deny certain web browsers, instant messengers, etc. Ideally, something to restrict what kids can and can’t access. It could be called something like Comodo Guardian or Comodo Parental Control.
+1… K9 is excellent,I have it installed on both my children’s PC’s, there used to be a conflict with Comodo and K9 a year or so ago but I can happily say that there is no issue any more, they both work perfectly together.
You could also try OPENDNS and select different options (adult material ETC) to be blocked
If you are not PC savy then the easiest to use is K9.