The ability to delay gratification has been shown to be related to higher education and income and better health status. We study in an experiment with 336 kindergarten children, aged three to six years, whether intertemporal choice behavior is malleable. In a control condition, about 50% of children prefer two rewards the next day over one reward immediately. By setting a simple default this fraction increases to more than 70%, indicating that simple defaults work very successfully in promoting delay of gratification. We also find that patience increases with age and that more patient children have a lower BMI.