In order to better understand obesity in preschool age and how to prevent and treat it, it is necessary to first familiarize yourself with the meanings of obesity, body mass index and the term preschool age. The aim of this paper is to study previous research in this area and to do our own research on the proportion of obese children in 2023 in the Republic of Croatia. Four kindergartens from continental Croatia participated in the research, and it was determined that about 10% of preschool children are overweight or obese, looking only at weight, and looking at the body mass index, 22% of children belong to the group of overweight or obese. The paper also deals with topics such as the causes and risk factors of obesity in preschool age, obesity prevention through eating habits, the role of educators in eating habits and physical activity of preschool children. In addition to prevention, the topic of treatment of obesity in children and their age and the importance of awareness of the parents of obese children about the seriousness of obesity and the treatment itself were also discussed.