This thesis generally speaks about the concept of obesity, as well as the causes, consequences, and prevention of obesity. The purpose and goal of this thesis are to determine the importance of the connection between parents, preschool teachers, and public health institutions in order to prevent and treat obesity in preschool-aged children. A study by the Institute of Public Health throughout Croatia showed a significant increase in obesity in preschool-aged children, reduced physical activity, and more use of digital media and eat almost no fruit or vegetables. That is why it is essential, by means of the joint efforts of the health institution, kindergartens, and parents, to work on improving the health condition of the preschool-aged child. The thesis describes an interview with a preschool teacher, parent, and health care worker in an early childhood institution. Interviews showed that the mutual cooperation of kindergartens, public health institutions, and preschool teachers was important. But there was a need for even stronger collaboration among the three factors. Together they form a triadic relationship. A preschool teacher with its creative approach and flexibility can be a support to parents. Public health institutions can be helpful with their expert and health advice. However, the main promoter of a proper and healthy diet is the parents with the respect that it is a key that parents represent a model of nutrition for the child. Of course, the family, kindergarten, and family surrounding should be included in continuous prevention programs in order to reduce the incidence of obesity in the population of preschool-aged children