Preventing sedentary behavior and adiposity in childhood has become a public health priority. We examined urban social and built environment characteristics as correlates of physical activity and anthropometry among 428 preschool children from low-income families in New York City. We measured the children's height, weight, skinfold thicknesses, physical activity by accelerometer, and covariates. We geocoded home and Head Start center addresses and estimated the following for an area within 0.5 km of those two locations using a detailed geographic database: neighborhood composition, walkability, crime and traffic safety, and aesthetic characteristics. Generalized estimating equations were used to examine the associations of area characteristics with physical activity or adiposity, adjusted for characteristics of the child, mother, and home. Participants were 2-5 years old, 53% female, 83% Hispanic, and 43% either overweight or obese. Of the walkability indicators, land use mix was associated with physical activity (26 more activity counts/minute per standard deviation increase in mixed land use, p = 0.015) and subway stop density was associated with adiposity (1.2 mm smaller sums of skinfold thicknesses sum per standard deviation increase in subway stop density, p = 0.001). The pedestrian-auto injury rate, an indicator of traffic safety problems, was associated with physical activity and adiposity (16 fewer activity counts/minute, p = 0.033, and 1.0 mm greater skinfold thickness per standard deviation increase in pedestrian-auto injuries, p = 0.018). Children living in areas with more street trees were more physically active and those living in areas with more park access had smaller skinfolds. However, many of the tested associations were not statistically significant and some trends were not in the hypothesized direction. Efforts to enhance walkability, safety, and green spaces in the local environment may be relevant to physical activity and adiposity, and therefore to the health of preschool-aged children from low-income families.