The concept of aggression can be found in everyday speech, and it is a very complex phenomenon that has been researched for many years and was introduced through out the different theories. A review of definitions and theories of aggression reveals that most authors agree that aggression is causing harm to another person, on the other hand not all of the authors agree that the aggression is carried with a purpose. The most important theories to which we devoted our attention are: instinctual theories, situational theories, the theories of aggression (as a learned behavior), cognitive, biological and physiological theories of aggression. In this paper, we mainly relayed on the work,knowledge and opinion of M. Žužul. According to M. Žužul, aggression is defined as each reaction performed with the intent to cause damage or injury of any kind. We also presented the most important factors that affect the occurrence and development of aggressive reactions. They are: emotional-motivational, cognitive-informational, social and situational and different types of aggression, which are classified according to form and function. We divided aggression to physical and verbal aggression,while Žužul stated that children's aggression is still divided into instrumental, hostile, defensive and aggressive play. This paper describes a research based on the development of violent reaction and its stability covering age and gender differences through the period of development. We point out that there is usually no difference in behavior between male and female kids, although there are some exceptions which are visible only in the preschool age. We also emphasize the importance of reacting on time and identification and responding to the aggression of educators in kindergarten. The biggest impact on aggressive reactions with children is caused by observation of the peers and violent and aggressive television programs. Prevention of any antisocial behavior is very important, as well as in case of aggression. Most often it is divided into primary and secondary, depending on the severity of aggression with children. The most important role in solving the problem of aggression has primarily family, but also kindergarten and educators.