In the Ballabeina study, we investigated age- and BMI-group-related differences in aerobic fitness (20 m shuttle run), agility (obstacle course), dynamic (balance beam) and static balance (balance platform), and physical activity (PA, accelerometers) in 613 children (M age = 5.1 years, SD = 0.6). Normal weight (NW) children performed better than overweight (OW) children in aerobic fitness, agility, and dynamic balance (all p less than 0.001), while OW children had a better static balance (p less than 0.001). BMI-group-related differences in aerobic fitness and agility were larger in older children (p for interaction with age = 0.01) in favor of the NW children. PA did not differ between NW and OW (p greater than or equal to 0.1), but did differ between NW and obese children (p less than 0.05). BMI-group-related differences in physical fitness can already be present in preschool-age children. (Contains 2 tables and 1 figure.)