I chose the topic of "Obesity in children" because obesity is a growing problem in the world. Obesity is also a big problem in Croatia, as we are the 5th country in Europe in terms of obesity. In this paper, I want to explain what exactly obesity is and why a healthy diet and exercise are important in obesity prevention. Obesity is increasingly occurring at an early age, in children and adolescents. Therefore, obesity prevention programs are implemented in pregnant women, because it is believed that obesity can occur as early as prenatal age. All of this is due to today’s fast-paced, modern lifestyle, which leads to unhealthy foods and insufficient physical activity which lead to obesity. In order to calculate obesity, it is necessary to calculate the body mass indexor BMI, and it is obtained by dividing body weight in kilograms by the square of body height in meters.