Executive functions (EFs) may help children to regulate their food-intake in an "obesogenic" environment, where energy-dense food is easily available. There is mounting evidence that overweight is associated with diminished hot and cool EFs, and several longitudinal studies found evidence for a predictive effect of hot EFs on children's bodyweight, but longitudinal research examining the effect of cool EF on weight development in children is still scarce. The current 3-year longitudinal study examined the effect of a latent cool EF factor, which was based on three behavioral EF tasks, on subsequent mean levels and 3-year growth trajectories of body-mass-index z-scores (zBMI). Data from a large sample of children, with zBMI ranging from normal weight to obesity (n = 1474, aged 6-11 years at T1, 52% girls) was analyzed using structural-equation modeling and linear latent growth-curve modeling. Cool EF at the first wave (T1) negatively predicted subsequent zBMI and zBMI development throughout the 3-year period in middle childhood such that children with better EF had a lower zBMI and less steep zBMI growth. These effects were not moderated by the children's age or gender. In conclusion, as early as in middle childhood, cool EFs seem to support the self-regulation of food-intake and consequently may play a causal role in the multifactorial etiology of overweight.