The article concerns children's aggressive behavior. Definitions of aggression and sources of its origin offered by different authors are examined here. There are given kinds of aggressive behaviour and examined reasons causing children's aggression.

Origin of children's aggressive behaviour is related with family and factors connected with early childhood. In family factors are examined child's and parent's relationship; style of family management; full and not full family; sister-brother relationship. And in factors connected with early childhood matter concerns coeval relationship; paying attention to adults' aggression; mass media.

As a rule aggressive children grow in families where exists a large distance between children and parents, children do not get enough cordiality, parents do not take interest in children's development, attention is not paid to the child's aggressive behaviour and where physical punishment is used for child's upbringing.

Study of early influence on aggression formation is important as aggression is stable in time and does not depend on situation. Aggressive children develop into aggressive youths and adults.