1. I know for OS 9 & earlier there was a utility which could tell you what changes had been made to your system ... all new files, etc. But for OSX I haven't come across this utility. But one may exist.

2. ONe thought is to lock the preferences file. However I have a suspicion LW will detect that as soon as attemepts to open & may not open at all. This move would also render junk filters unusable. So AFAIK I don't know of how it oculd be done. For a start I think it would be best if they used their own user account. Then you can set the filters as you desire .. such as blocking out porn & some spam. The following link is a guide to help you doing that Direct instructions to eliminate porn from results