From the moment they started a Facebook or other social media account, you should be able to observe what is going on digitally in your child's life. It isn't about snooping -- it is about being a responsible parent.
I don't like Facebook, and I don't trust Facebook. You don't even need an account to be punked by Facebook. Facebook doesn't know who is real and who isn't real. Many people may not even be aware there is an impostor profile of them on Facebook.