One group of children watched an adult model physical and verbal aggressive behavior. The second group watched a “peaceful” model. And a third group didn’t watch anybody. The study found that children in the “aggressive” group often imitated aggressiveness when they played with a doll, more so than the other groups.
The aggressive behavior of an adult had a greater impact on boys than girls.
Bandura, A., Ross, D., & Ross, S. A. (1961). Transmission of aggression through imitation of aggressive models. The Journal of Abnormal and Social Psychology, 63, 575-582.