The prevalence of obesity among children and adolescents is increasing rapidly. In Germany, between 10 – 20% of children are overweight or obese. Besides, a possible genetic predisposition and excessive energy intake, decreased physical activity and a sedentary lifestyle have been implicated as risk factors. Data about childrens activity and its correlation with obesity are sparse and also inconsistent, as different measurement criteria are used. Some authors found differences between the fitness of obese and non-obese children, while others did not. Several studies described worse results in motor abilities with overweight children compared to their normal weight counterparts, especially in coordination and endurance performance. There is a general agreement that obese children prefer sedentary habits, mainly audio-visual media like television and PC. The incidence of obesity increases with a daily television consumption of more than five hours. But to what extent, with what intensity, and which sports/exercise techniques are suitable and necessary for preventive measures is not precisely known. As a result, recommendations for daily routine and physical activities as well as minimal requirements can hardly be formulated. This paper presents the current aspects of the role of physical activity in the development and prevention of overweight and obesity during childhood.