In children - particularly those going through the hormonal changes of puberty - it's not always easy to differentiate between sadness or moodiness and depression.
But parents should think about taking a child for help if the symptoms last for around two weeks, said Dr. David G. Fassler, author of a book on childhood depression called "Help Me, I'm Sad."
Depression symptoms include markedly diminished interest or pleasure in daily activities, depressed mood and significant changes in weight and appetite. Other symptoms are insomnia, slow physical movement, fatigue, feelings of worthlessness, diminished ability to concentrate and recurrent thoughts of death.
Prompt treatment is important, he said, because even though one bout with depression may resolve itself within nine months, depression is thought to be a chronic problem that recurs throughout life.
With proper care, parents and children can best learn how to manage the disease.
Here's a test to see if your child is clinically depressed. If your child answers - or if you think your child would answer "true" to three or more items, he or she should be evaluated by a qualified mental health professional. If your child answers "true" to item 13 about self-destructive or suicidal behavior, seek help immediately.
1. I feel sad lots of the time.
2. I have trouble sleeping.
3. I feel tired lots of the time.
4. I don't have many friends.
5. I cry a lot.
6. I don't like playing with other kids.
7. I don't feel as hungry as I used to.
8. Other kids don't like me.
9. I feel lonely.
10. I have lots of headaches and stomachaches.
11. I don't like school.
12. I have bad dreams.
13. Sometimes I think about hurting myself.
14. I worry a lot.
15. I don't like myself.
16. Other kids have more fun than I do.
17. I don't do as well in school as I used to.
18. Sometimes I have trouble concentrating.
19. I feel angry lots of the time.
20. I get into lots of fights.
Source: "Help Me, I'm Sad," a new book on childhood depression by Dr. David G. Fassler.