Childhood is an ecologically and socially mediated component of life history. Among prehistoric foragers from the Late/Final Jomon period (3400 to 2300 BP), socially visible identities associated with childhood begin at approximately 2.0 years, while ecologically identifiable childhood begins at approximately 3.5 years. Incremental microstructures of enamel were evaluated for evidence of linear enamel hypoplasia (LEH), and age-at-defect formation was estimated in the dental remains of these individuals. Interquartile ranges for age-at-defect formation were between 2.8 and 4.1 years, while 90% confidence intervals were between 2.1 and 4.8 years. The number of LEH formed during these ages was, however, neutral with respect to mortality. These results argue that the transition from infancy to childhood was a period for increased growth disruption among these prehistoric foragers, although these disruptions did not influence mortality patterns. These findings suggest that the stress experienced during the infancy/childhood transition was incorporated into the Jomon physiological system in such a way that it did not diminish energetic investments into surviving future stress events.