nooooo
other 'friends', or 'friends of friends' walls can be vile and awful (voice of experience
) and absolutely not ok for younger kids.
Would only let my kids join facebook this young by insisting that they made me one of their 'friends', and told them I'd be monitoring their facebook activities (=stalking them online). They stayed pretty well behaved.
Had a bad incident though with mother of another boy who tried to tell me my youngest ds had been obscene to her son online. But because I could track all my son's activities, I soon found out what had actually happened - it was her son who was being vile, swearing, saying vile things to my son, not my son causing trouble.
I can't stand facebook, causes too much trouble and stress ime.