The object of this paper is to learn what little children know about the inside of their bodies before they have studied these particular aspects at school. The data for our project were collected by means of drawings made by 342 Spanish children aged four to seven. They were required to depict where the food, drink, and air which enter their bodies go. In addition to this, we intend to study how the ideas of children evolve during three consecutive years. For this purpose, a group of 32 subjects was monitored. Our findings show that the children recognise specific organs in their own bodies which they associate with the intake of food and air. Furthermore, they usually extrapolate those organs to other animals they are familiar with. Their ideas about the digestive system are more adequate than the ones about the respiratory system, though their ideas improve as they become older, above all those concerning the digestive system. Taking these findings as a basis, this paper suggests some points to be taken into consideration for teaching purposes. (Contains 6 tables and 3 figures.)