ABSTRACTThe acquisition of social‐emotional competence (SEC) in early childhood has implications for critical child and adult outcomes, such as school readiness, educational and occupational attainment, and mental health. To elucidate this developmental process, normative trajectories of social‐emotional competence in infants and toddlers were modeled using longitudinal mixed effects modeling, including the evaluation of child and family characteristics as moderators. The SEC of 12–36‐month‐old children (N = 256, 83% White, 51% female) was assessed in a cohort‐sequential design using the Infant Toddler Social‐Emotional Assessment Competence scale. Trajectories were modeled using linear, quadratic, exponential, and logistic mean forms. Following base model selection, child sex, maternal education, parental occupation, family income, and number of siblings were separately added to the model to assess their effect on trajectories. Results show that infants and toddlers SEC follows a quadratic pattern of growth. Additionally, girls had higher scores than boys at 12 months with similar slopes. Number of siblings was also significant at 12 months such that children with fewer siblings had higher scores than those with more with similar slopes. This suggests a female advantage in early SEC acquisition exists even before 12 months and that sibling number may moderate SEC in infancy and toddlerhood.