Childhood depression is different from the normal "blues" and everyday emotions that children go through as they develop. Just because a child seems sad doesn't necessarily mean they have significant depression. But if the sadness becomes persistent or interferes with normal social activities, interests, schoolwork, or family life, it may mean they have a depressive illness. Keep in mind that while depression is a serious illness, it’s also a treatable one. The symptoms of depression in children vary. The condition is often undiagnosed and untreated because symptoms 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 happen, 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.