Obesity as an epidemic has affected the human population over the last few decades. Sedentary lifestyle, increasing availability of food, especially nutritionally poor foods lead to increased energy intake. It is important to react from the earliest age of the child, so prevention is key to reducing obesity in both children and adults. Obesity is a complex multifactorial disease that develops under various factors, genetic, metabolic, environmental, and bad life habits. Obesity occurs when the intake of energy, specifically food, is higher than the energy consumption. Excess energy is then stored in the body in the form of fat cells, or fat. Fat mostly accumulates in adipose tissue, but also in internal organs such as the liver and musculoskeletal system. The distribution of adipose tissue throughout the body is genetically determined, and differs by sex. Childrend's diet must be rich in all kinds of micronutrients and macronutrients, since it is a period of growth and development. It is important that their diet is as varied as possible. In addition to diet, reduced physical activity also contributes to weight gain. Children spend more and more time in sedentary activities instead of physical activities. The purpose of this paper is to determine the relationship between children's lifestyle, eating habits and physical activity of preschool children, with the child's body mass index, and parents' attitudes about the importance of proper nutrition and physical activity of the child. The results of the research showed that children who consume fruits and vegetables on a daily basis have a lower BMI, in contrast to those children who do not eat fruits and vegetables every day. The survey also showed that children who engage in organized physical activity outside kindergarten have a more normal BMI than children who do not engage in organized physical activity. In order to prevent the development of children's obesity, the family is most important, mostly the parents. Therefore, parents' attitudes about the importance of nutrition and physical activity were examined, and the results show that children of parents who are aware of the importance of proper nutrition from an early age had a more normal BMI than those who were less aware of the importance of proper nutrition.