Iron deficiency anemia during infancy is associated with delayed psychomotor and cognitive development; thus there is global interest in improving infant iron status through iron supplementation programs early in life. In adults, iron homeostasis primarily is controlled through regulatory changes in iron absorption; however, there is little understanding of mechanisms that regulate iron absorption in infants. As iron stores become depleted from rapid hemoglobin expansion, ontogenic transition to regulated iron absorption must occur. To elucidate age-dependent mechanisms regulating intestinal iron absorption and homeostasis in human infants, studies in suckling rat pups indicated that increased divalent metal transporter 1 (DMT1), ferroportin 1 (FPN1), and hephaestin expression and changes in localization within the enterocyte may direct the ontogenic regulation of iron homeostasis mechanisms. Unlike observations in adults, iron absorption, DMT1, and FPN1 expression were not affected by iron intake during mid-infancy, similar to observations in human infants. Interestingly, at this age supplemental iron was retained in the small intestine, but only in pups that were not previously iron deficient. Although intestinal retention may possibly help limit excess iron absorption, decreased linear growth, head circumference, and weight gain has been observed in iron-supplemented, nonanemic human infants, suggesting that global iron supplementation programs should be approached with caution.