Obesity is undoubtedly one of the biggest medical problems of the 21st century. Regrettably, the problem affects more and more children and adolescents. 10% of world's school-aged children have an excess body weight and a quarter of these children are obese. In Europe every fifth school-aged child suffers from an excess body weight. The prevalence of overweight and obesity among Polish adolescents is about 14%. An excess body weight can be the consequence of genetic factors, endocrine disorders or certain drugs. However, "simple obesity" is the most common, consequence of providing too much energy from food products in comparison to energy expenditure (caloric excess). Today's lifestyle promotes the development of obesity. The lack of physical activity, sedentary lifestyle and energy-rich diet are the main causes of an excess body fat accumulation. Because of improper eating behaviours children consume an excess amount of energy; and their diet is deficient in elements necessary for proper development. The examples of such bad eating habits are: snacking highly processed and calorie-rich foods between meals eating in front of the TV screen, skipping breakfasts, drinking sugar-sweetened beverages, "eating out" frequently and "emotional eating". Bad eating behaviours are crucial factors for the development of obesity. Eating habits are usually formed in early childhood and parents play a very important role in their development.