This study is aimed at finding preconceptions of preschool children about the functioning of the human body. It is divided into three parts. The first part presents theoretical background and highlights the importance of children's preconceptions for the children's learning process. The second part presents a variety of empirical surveys that demonstrate possible methodological approaches. The third part presents qualitative research using conceptual mapping methods, analyses of children's drawings and interviews with children. Research findings are presented in the conclusion and some structures of children's preconceptions about respiratory, circulatory and digestive systems are described.