Research Findings: Preschools have many norms and rules children are supposed to follow. Among them, behavioral norms associated with mealtime are of great consequence because eating is an essential life function. The present study examined young Japanese children's understanding of hygiene norms and rules at mealtime from the standpoint of their awareness of contamination. Previous studies on contamination sensitivity have mainly focused on children's knowledge itself and have paid little attention to the origins of such knowledge. However, the present study examined how adults talk to children about contamination as 1 possible source of children's knowledge. Practice or Policy: Study 1 involved 32 days of observations during lunchtime at 3 Tokyo preschools. The teachers frequently told children to adhere to hygiene habits such as washing their hands. Although preschool teachers attached much weight to hygiene, their explanations were not precise. They often used 1-word or 1-phrase directions (e.g., "Dirty") or just input-output explanations such as "Please wash your hands, or you'll get sick." Explanations of why breaking hygiene norms would lead to sickness were seldom offered to children. In Study 2, 26 children age 3 ([average] age = 3.7) and 22 children age 5 ([average] age = 5.7) were asked to explain why breaking hygiene norms would lead to sickness. In contrast with teachers' simple expressions in Study 1, even 3-year-old children frequently generated contamination mechanism explanations (e.g., referring to germs and disgust transmission spontaneously). (author abstract)