From 1965--1975 the food intake and energy supply of children aged 2--14 years in families of different social classes were studied with the precise weighing method. The individual child was surveyed on an average of 21--42 successive days. Energy intake increased from 1450 for boys aged 2--3 years to 2600 kcal/day for boys aged 12--14 years, girls of the same age had an energy intake between 1300 to 2400 kcal/day. The differences between boys and girls regarding energy intake, absolute and per kg body weight, are shown. Our results of the energy intake are representative for children of the same age groups in other highly industrialized countries. The energy intake of preschool-children was equally distributed among 4 meals per day, whereas in school-children it was distributed among 5 meals with different energy contents. 35--50% of the energy supply is of animal origin, 60--65% of vegetable origin. The contribution of different food groups to the energy supply and the differences in the intake of these food groups between pre-school-and school-children are demonstrated. For the individual child a survey period of 21--28 days is necessary to obtain its individual average energy intake with the maximum standard deviation. The significance of general averages for the energy supply of age groups regarding the individual child is discussed. The day to day variations of energy intake in children are shown. The significance of these variations for nutrition in health and disease is discussed.