The causes and manifestations of depression in children are different at different times. Depression is mostly caused by psychological stimuli, such as separation from parents, parental discord, lack of family warmth, excessive punishment, abuse, abandonment, rejection, bullying and ridicule at school, academic failure, and failure to achieve desired goals. In general, depression occurs mostly in adolescents, but can occur from infancy to adolescence. It is more frequent in girls than in boys. The main manifestations are depressed mood, no sense of cheerfulness, crying, temper tantrums, no interest in fun, reduced speech, reduced thinking ability, low self-esteem (thinking they are stupid, foolish, ugly), loneliness, self-loathing, even self-harm and suicidal behavior, loss of appetite, significantly reduced energy, less or significantly more activity than usual, insomnia, early awakening or excessive sleep. Older children may behave in a disciplinary manner, truancy, fighting, poor partnership with, and decreased academic performance. Depression in younger children can be classified as acute, chronic, or insidious. Acute depression has obvious mental factors before the onset, such as the sudden separation of parents or people with whom the child is most attached, serious illness, sudden death of a loved one, and unexpected disasters. Chronic depression is the frequent or long-term presence of adverse stimuli. Depression arises gradually, and the child itself is more sensitive and introverted, and is accompanied by some somatic discomfort in addition to a bad mental state. The psychological stimuli of insidious depression may not be obvious and the child’s depression is not obvious, often manifested by some behavioral problems such as hyperactivity, aggressive and disciplinary behavior, learning difficulties, and unexplained headache, abdominal pain, and loss of appetite. Depression in infancy is mainly caused by separation from the mother, which first manifests as incessant crying, searching for the mother if the child can already walk, and poor mood and agitation; after a few days, it turns into depression, withdrawal, loss of interest, lack of appetite, and poor sleep. After a few days, depression, withdrawal, loss of interest, lack of appetite, and poor sleep, improve after reunification with the mother. Depression in preschoolers is characterized by frequent crying, little talking, unhappy faces, lack of interest, decreased appetite, decreased sleep, not playing with children, withdrawal, and decreased activity. Depression in school-age children may also include low self-esteem, complaining, self-blame and guilt, inattention, memory loss, slow reaction time, decreased thinking ability, significant decline in academic performance, thoughts of lightness of life, and even suicidal behavior. In addition to the above symptoms, depression in adolescents can include aggressive and destructive behavior, as well as truancy, absenteeism, smoking, alcohol, drug and substance abuse.