Acutely and critically ill children, like adults, want information about their illness. Children put information they gather into the context of their understanding of the world around them, which is influenced by their level of cognitive development. The development of their understanding of the world is also apparent in their understanding of their bodies and of illness etiology, prevention, and cure. Research generally supports the expected developmental progression of children's understanding of body parts and functions and of illness etiology. Implications for practice are provided.