Children who are iron deficient (ID) or iron-deficient anemic (IDA) have been shown to seek and receive less stimulation from their caregivers, contributing to functional isolation. Over time, the reduced interactions between child and caregiver are thought to interfere with the acquisition of normative social competencies and adversely affect the child’s development. The current study examined functional isolation in children who were ID or IDA in infancy in relation to social difficulties in middle childhood and problem behaviors in adolescence. Using a sample of 873 Chilean children, 45% of whom were ID or IDA in infancy, structural equation modeling results indicated that infant IDA was associated with children’s dull affect and social reticence at age 5, which were related to mothers’ unresponsiveness and understimulation. Mothers’ limited responsiveness and stimulation were, in turn, related to children’s peer rejection at age 10, which further linked to problem behaviors and associating with deviant peers at adolescence. Findings support the functional isolation hypothesis and suggest that early limited caregiver responsiveness and stimulation contribute to long-term social difficulties in adolescents who were iron-deficient anemic in infancy.