The symptoms of depression in children vary. It is often undiagnosed and untreated because they are passed off as normal emotional and psychological changes. Early medical studies focused on "masked" depression, where a child's depressed mood was evidenced by acting out or angry behavior. While this does occur, particularly in younger children, many children display sadness or low mood similar to adults who are depressed. The primary symptoms of depression revolve around sadness, a feeling of hopelessness, and mood changes.