This was a very sad documentary. It's sad that a child ever goes through something like that. It's sad that because of abuse from someone else, they feel they need to abuse others. It's sad that they don't know how to love or let others love them. I wish that things were different in this world.
I know it happens a lot though. I've seen and heard about several cases like this and even met some of the children; because my aunt worked for Head Start (they work with CPS), and because a couple of my ex-boyfriends were in situations like this. One of their adopted parents was a foster parent to several children who came from abusive parents. Also I live three houses down from a family with quite a few foster children. I've also had a few friends that were abused when they were little and then adopted.
One of these friends had to go through a lot of therapy and counseling for some of the emotional scaring. This helped, but would never make him forget what had happened to him. He was not a very trusting or loving person toward anyone, and could be very aggressive and abusive if provoked even by the smallest thing.
Self-esteem is one of the most important things a child can have and get from their caregivers, and it is also a very hard thing to change from negative to positive. When parents are abusive the child almost definitely will have a negative self-esteem. This causes life long problems for any child.
This world is a scary place and to think that some children are born into families where they can't feel safe makes it a sad place too. I wish things were different, but since they aren't we...