To examine the effects of child age and birth order on sensitive parenting, 364 families with 2 children were visited when the second-born children were 12, 24, and 36 months old, and their older siblings were on average 2 years older. Mothers showed higher levels of sensitivity than fathers at all assessments. Parental sensitivity increased from infancy to toddlerhood, and then decreased into early childhood. The changes in parental sensitivity with child age were similar for mothers and fathers, and mothers' and fathers' sensitivity levels were related over time. However, the changes in parental sensitivity toward the firstborn and second-born child were not related to each other, suggesting that parents' experiences with the firstborn child do not have implications for their sensitivity toward their second-born child. Instead, the child's own unique characteristics and developmental stage seem to play a more important role. These findings highlight the importance of considering developmental child characteristics in the study of parenting, and suggest that individual differences in attaining developmental milestones may affect parental sensitivity.