As a webmaster I can mention methods to check your child's computer and find if something they are doing worths your attention.
- Enable "save chats history" in all messenger applications so you can access them later.
- Download Google desktop. Google desktop is very good to browse/find all existing documents, emails in cache and chats as well. To find possible interesting stuff try to look for specific keywords like: sex, love, meet, kiss, date, go out, etc... use keywords that might be present in a conversation, email, word document, etc between your child and a possible pedophile. The most important issue that you need to take care of is "MONITORING YOUR CHILD'S BROWSING and CHAT'S HISTORY.
- If you use Bellsouth they provide you with a tool "Parental Controls" to limit access for specific accounts on specifics services.
- The other option is to use AOL's "Parental Controls" if you don't have a bellsouth account. This is free and would do the job, download it at http://daol.aol.com/safetycenter/
- If you don't like the two options above use this free service which I heard is good. http://www.hoopaa.com/
As a regular guy I can tell you that all the above is useless if you don't teach your child how to react and what to do if there are suspicious people trying to contact them. Teach your child not to share personal information with anyone, not to accept invitations from someone they don't know, to mention allways their internet activities, not to hide any secret from parents and the most effective method of all... is a good relationship between you and your child based on trust.
Hope my answer helps ;)