Is Facebook safe for children?

Both my children are under age and I have permitted them both to have facebook accounts. I have both username and pwords of both children, they do not friend or accept a friend request without asking my permission. They have no friends I don't know about or know personally. Both my children are very responsible and I trust them 100%, they are 11 and 10yo respectfully. Most of their FB friends are my FB friends, so what they see, I see. So if something is posted that I don't like or is inappropriate for them, I will log into their accounts and delete it before they get to see it. Maybe FB is unsafe for some underage children, but that is because they are not treating it with respect and their parents are not monitoring their accounts. That makes it hard for those of us who are...