I'm friends with my sons and DDILs. I didn't realize that when you set up your account and give permission to access your E-mail contacts, it automatically notifies everybody in your address book to befriend. I had some old contacts that I would have never thought to have added.
As far as my adult kids, it has caused me a few problems when I read something that upsets me - nothing major. Since setting up, I haven't initiated adding any of their friends, but accepted if they requested me as a friend.
I need to read "Facebook for Dummies"! (I have it, just haven't looked at it much.)