To evaluate whether parents who assess their infants as more developmentally advanced are more likely to begin feeding their infants complementary foods before 6 months, and whether developmental readiness explains racial and ethnic differences in complementary food introduction.

In a cohort of mothers of 5475 infants from New York state, 9 markers of infant development and timing of initiating complementary feeding were assessed. Mixed effect models assessed associations between developmental markers and initiation of complementary feeding before 6 months term-corrected age. Direct and indirect effects of racial and ethnic differences in complementary feeding through a total development score were computed.

In a fully adjusted model, infant sitting (aOR: 1.60, 95% CI: 1.32, 1.93), head control (aOR: 1.51, 95% CI: 1.26, 1.81), reaching (aOR: 1.19, 95% CI: 1.04, 1.37), mouthing (aOR: 1.26, 95% CI: 1.08, 1.46), and having a good appetite (aOR: 1.61, 95% CI: 1.15, 2.24) were uniquely associated with complementary feeding before age 6 months. A 1-point increase in a total development score was also associated with higher odds of complementary feeding (aOR: 1.26, 95% CI: 1.19, 1.33). The development score explained some racial and ethnic differences in the odds of complementary feeding before 6 months.

Results suggest that parents are using their children's developmental markers to decide when to begin complementary feeding. Furthermore, observations of racial and ethnic differences in the timing of complementary feeding may be explained by perceptions of developmental readiness, in line with recommendations. Future research on complementary feeding should incorporate assessments of infant developmental readiness.