Childhood obesity is a major problem worldwide and a key contributor to adult obesity. This research explores caregivers’ lay beliefs and food parenting practices, and their long-term, intergenerational effects on their children’s food consumption and physiology. First, a cross-cultural survey reveals the link between parents’ belief that tasty food is unhealthy and the use of extrinsic rewards to encourage their children to eat healthily, with adverse downstream consequences for the children’s body mass indices. Next, two studies demonstrate the mechanism by which this strategy backfires, as providing extrinsic rewards ironically increases children’s unhealthy food consumption, which in turn leads to an increase in their body mass indices. The final two studies demonstrate potential solutions for public policy and health practitioners, either by manipulating “unhealthy = tasty” beliefs directly or by breaking the association between these food beliefs and the use of extrinsic rewards through an intervention.