Gerstadt, Hong, and Diamond (1994) investigated the development of inhibitory control in children aged 3½ – 7 years using the day–night task. In two studies we build on Gerstadt et al.'s findings with a measure of inhibitory control that can be used throughout childhood. In Study 1 (twenty-four 3½-year-olds and sixteen 5-year-olds) we modified Gerstadt et al.'s day–night task. Using this modified task we obtained further evidence for the development of inhibitory control in children between 3½ and 5-years-old. We also obtained data suggestive of more moderate working memory development. In Study 2 we tested 84 children aged between 3½ and 11 years. The aim was to determine how much inhibition and working memory taxed children of different ages. We obtained evidence that inhibitory demands were high and that inhibitory development was non-linear, with rapid improvements in children between 3½ and 5 years and only modest improvements thereafter. In contrast, working memory demands were low and working memory development was more linear. We interpret these findings as evidence that working memory has relatively little impact on performance in our modified version of the day–night task.