A、The child seems sad. B、His or her sadness lasts for a rather long period of time. C、The child occasionally feels blue or down.

My child seems sad; is he suffering from depression? Not necessarily! Normal sadness or grieving is not depression.  Don’t worry if your child occasionally feels blue or down in the dumps.  Life has its ups and downs, and it’s normal for children to grieve over a loss or feel sad for a few hours or days at a time. But [32] if his melancholy (忧郁症状) lasts for more than a couple of weeks or seems to interfere with his regular activities and relationships, he may be clinically depressed. Depression is far more than a temporary change in mood; it’s marked by a sense of hopelessness and a lack of energy and enthusiasm that can last for weeks, months, or (in rare cases) even years at a time. [33] The good news about depression is that it’s almost always treatable. The key is identifying the problem and getting help.
   What are the symptoms? It might seem logical that the most obvious symptom of depression would be sadness, but many depressed children say they don’t feel sad or gloomy. Interestingly, one of the key signs of depression in children is [34] irritability(易怒). Children may be depressed if [34] they have trouble getting along with other kids and family members or have dramatic swings in mood. Other signs of depression include lack of energy, inability to  concentrate,  [34]  poor performance in school,  a  sense of hopelessness  and  helplessness,  and  frequent  complaints  about  physical ailments like headaches or stomachaches.
   If your child exhibits any symptoms of depression, ask yourself three questions: [35] Is this behavior new? Is it long-lasting (going on for several weeks or more)? Are the symptoms interfering with his ability to function at home, in school, or with his friends? If you answer yes to any of those questions, you should probably have your child evaluated by a child or adolescent  psychologist,  psychiatrist,  or  other  licensed  mental  health professional trained to work with children and adolescents.