Growth curve models were used to examine the effect of genetic and ecological factors on changes in height and weight of 225 children from low income, urban families who were assessed up to eight times in the first 6 y of life. Children with early growth deficiency [failure to thrive (FTT)] (n = 127) and a community sample of children without growth deficiency (n = 98) were examined to evaluate how genetic, child and family characteristics influenced growth. Children of taller and heavier parents, who were recruited at younger ages and did not have a history of growth deficiency, had accelerated growth from recruitment through age 6 y. In addition, increases in height were associated with better health, less difficult temperament, nurturant mothers and female gender; increases in weight were associated with better health. Children with a history of growth deficiency demonstrated slower rates of growth than children in the community group without a history of growth deficiency. In the community group, changes in children's height and weight were related to maternal perceptions of health and temperament and maternal nurturance during feeding, whereas in the FTT group, maternal perceptions and behavior were not in synchrony with children's growth. These findings suggest that, in addition to genetic factors, growth is dependent on a nurturant and sensitive caregiving system. Interventions to promote growth should consider child and family characteristics, including maternal perceptions of children's health and temperament and maternal mealtime behavior.