Something that has gone on for generations and seems to be getting worse today is the problem of bullying, because there are an awful lot of undisciplined children. Often, if your child is being bullied, they won't talk about it. They won't come home and tell you this.
What if someone is picking on your child? You will begin to see that maybe they don't want to participate the way they used to. They'll show signs of depression, anger and withdrawal.
Understand this is not a natural progression. We say, "Let kids work it out." If somebody is picking on your child, and they're being bullied, you need to get involved.