Depression is one psychological disorder that most people have some ideas about since we all have been sad. But clinical depression is far from normal. Several different symptoms are noteworthy and they must persist for a substantial period of time, as well as significantly interfere with work or other important functions. People who are clinically depressed stop enjoying things, and typically just have trouble facing each day. Children can get depressed clinically as well, however it doesn't always look like adult depression.
Childhood depression is noteworthy for some age specific features, including acting out.
Many children who get picked on routinely are depressed. You might be surprised at the relatively high number of children who are suicidal and whose parents may not even suspect. David J. Berndt and Charles Kaiser, however there are other good measures as well. More can be found on this in the pages on psychological testing. Dr. Berndt received his Ph.D. from Loyola University of Chicago.