Obesity is increasingly becoming a problem for Western societies, to the extent that politicians, scientists, patient organisations and the media now refer to it as 'the obesity epidemic'. Concerns about the damaging effect of increasing body weight on public health has led to a strong growth in the amount of scientific work on the condition, with the medical professions leading the way. This article discusses that, first of all, scientific evidence for obesity-associated mortality is at best ambiguous, and proposes that at least some of contemporary medical preoccupation with obesity has a moral origin in that it seeks to correct unwanted or immoral behaviour. It then continues to reflect on the effect of the conceptual transformation of healthy children into patients, and concludes with some reflections on the ethical implications of the obesity disease for the wellbeing of children.