The measurement of cardiovascular functioning targets an important bridge between social conditions and differential well-being. Nevertheless, the biocultural, psychosocial processes that link human ecology to cardiovascular function in children remain inadequately characterized. Childrearing practices shaped by parents' cultural beliefs should moderate children's affective responses to daily experience, and hence their psychophysiology. The present study concerns interactions among family ecology, the normative social challenge of entry into kindergarten, and parasympathetic (vagal) cardiac regulation in US middle-class children (N = 30). Although parents believed children must be protected from overscheduling to reduce stress and improve socio-emotional adaptation, maternal rather than child schedules predicted parasympathetic regulation during a nonthreatening social engagement task following school entry. Children of busier married mothers, but less busy single mothers, showed the context-appropriate pattern of parasympathetic regulation, low respiratory sinus arrhythmia (RSA). These findings are expected if: maternal and family functioning, rather than the scheduling of the child's daily life, principally drive young children's cardiovascular responsiveness to a normative challenge; and busy schedules represent high family functioning with married mothers, but not under single-parent conditions wherein adult staffing is uniquely constrained. Family ecology is shaped by culture, and in turn shapes the development of children's cardiovascular responses. Appropriately fine-grained analysis of daily experience can illustrate how culturally driven parenting practices may have unintended consequences for child biological outcomes that vary by family structure.