Aggression is a pattern of behavior in children that parents don't well understand or tolerate. Children are often frustrated at an early age when trying to learn behaviors that correspond to their parents' expectations. Frustration of one's attempt to feel worthwhile and gain acceptance also often leads to unhealthy aggression. Most children who have low self-esteem tend to vent their hostile feelings against inanimate objects, rather than other people.
Children also learn aggressive behavior by observing others.
Some young people who have been bullied by older brothers and sisters imitate this behavior in dealing with children younger than themselves. Others will imitate their parents' methods of disciplining them as they interact with children of their own age. Children identify with adults and peers they love or admire. Sometimes they'll even imitate a person they fear. All children acquire many behaviors by copying what they see others doing.