Childhood obesity has multiple causes, most of them capable of explaining only one part of the problem. The population-wide impact of sedentary lifestyles and availability of energy-dense food is undeniable, but substantial individual differences in body weight persist, suggesting that individuals respond differently to the ‘obesogenic’ environment. One plausible mechanism for this variation is the early expression of appetitive traits, including low responsiveness to internal satiety signals, high responsiveness to external food cues, high subjective reward experienced when eating liked foods and preferences for energy-dense foods. Case–control studies support the existence of abnormalities in these traits among obese children compared with normal-weight children, and correlations between psychometric measures of child appetite and child weight suggest that appetitive trait profiles may not only promote obesity but also protect against it. The origins of appetitive traits are as yet uncharted, but will include both genetic and environmental influences. Parental feeding style may affect the development of appetite but the exact nature of the relevant behaviours is unclear and many studies are cross-sectional or begin late in childhood, obscuring causal relationships. Future research should explore determinants and biological mechanisms by using prospective designs beginning early in life, measuring relevant biomarkers such as gut hormones and incorporating neuroimaging and genotyping technologies. Potential clinical applications include the identification of ‘at risk’ children early in life and interventions to modify appetitive traits or ameliorate their impact on intake and weight.