Is a childhood always a happy time?

Recently I have read the patineuse's note about children.
http://www.italki.com/notebook/entry/147533.htm
How lucky children are who have parents and other relatives! They get so much love and attention.
My sister works in a children's home. She's a psychologist. She's currently working as a director's substitute. She told me many sad stories about the children who live there. It's very difficult to work in a children's home, but she really loves her job. Sometimes the children are awful, they are rude. It's difficult to control them. But they are just children. They are not little young.  They are all pupils, so they remember all the difficulties of their lives. They know why they are there. Their stories are usually so sad. Some parents are murderers, some ones are addicts. These children have seen many cruel things at the beginning of their during their short lives. So they often turn into hedgehogs to defend themselves. But in fact, they are really kind and hurtable easily hurt. Or:  It's easy to hurt their feelings.
I respect my sister's work! I respect her so much! She tries to find a way into each child's heart because there are no wrong bad children.