He often locks himself up in his room, and once didn't eat for a few days. Any child who has changes in his behavior or mood which are lasting and interfering with his life at home, in school or with his friends, should have an evaluation by a mental health professional. It could be a condition like depression, which is very treatable. I would talk to the child's doctor or school counselor and ask for help for a local referral. The important message for parents is that kids do get depressed.
Depression is a real illness and it's very painful.
But it's also very treatable. If you think your child may be depressed, get an evaluation. Help is available. Send them in. Browse through transcripts of our weekly health chats.