Dietary survey data show that intake of sugar-sweetened beverages is negatively associated with intake of milk, but these findings have yet to be confirmed by laboratory feeding studies. The objectives of the present study were to analyze children's intake across two laboratory-based ad libitum lunches to (a) investigate the relationships between intake of sweetened beverages, milk, and calcium, and (b) explore relationships between beverage consumption and child age and weight status. Data were extracted from a cohort of 126 3- to 7-year-old twins from diverse ethnic backgrounds who participated in a cross-sectional study (conducted from November 1999 to September 2002) designed to determine the genetic and environmental contributions to eating and body weight. At two visits, children ate ad libitum from lunches that offered a variety of sugar-sweetened and calcium-rich beverages. Total beverage and nutrient intakes were computed from the test meals. Weight, height, and waist circumference were assessed on the final visit. Regression analyses tested the associations among intake of sweetened beverages, calcium, and milk (primary aim), and whether these variables were associated with child age and weight status (secondary aim). Sweetened beverage intake was negatively correlated with both milk (P<0.01) and calcium (P<0.01) intakes, and these relationships remained after controlling for age, sex, and ethnicity (P<0.01). Child age was negatively associated with milk intake (r=-0.22, P<0.01) but positively associated with intake of sweetened beverages (r=0.27, P<0.01). Results support the notion that sugar-sweetened beverages displace milk in a single meal, and this phenomenon may vary with child age. Due to the cross-sectional nature of this study, future investigations are needed to determine the long-term implications of this consumption pattern. The possibility that limiting sweetened beverages may help optimize dietary calcium during childhood is a topic that merits further research.