Technical Abstract: OBJECTIVE: Whether developmental periods exist in which children become particularly sensitive to environmental influences on eating is unclear. This research evaluated the effects of age on intake of large and self-selected portions among children 2 to 9 years of age. RESEARCH METHODS AND PROCEDURES: Seventy-five non-Hispanic white children 2 to 3, 5 to 6, and 8 to 9 years of age were seen at a dinner meal in reference, large, and self-selected portion size conditions in which the size of an entree was age-appropriate, doubled, and determined by the child, respectively. Weighed food intake data were collected. Entree bite size and bite frequency were assessed. Height and weight measurements were obtained. RESULTS: The effect of age on children's intake of the large portion was not significant. Entree consumption was 29% greater (p < 0.001) and meal energy intake was 13% greater (p < 0.01) in the large portion condition than in the reference condition. Increases in entree consumption were attributable to increases in average bite size (p < 0.001). Neither child weight nor maternal weight predicted children's intake of large portions. Self-selection resulted in decreased entree (p < 0.05) and meal energy (p < 0.01) only among those children who ate more when served the large portion. DISCUSSION: The results of this research confirm that serving large entree portions promotes increased intake at meals among 2- to 9-year-old children. These findings suggest that any age-related differences in children's response to large portions are likely to be smaller than previously suspected.