We investigated conceptual overlap between literature demonstrating links between adult facial width-to-height ratio (FWHR) and behavior and that demonstrating links between infant FWHR and temperament by investigating whether babyfaceness is associated with FWHR and behavior at both ages. Babyfaceness was positively correlated with FWHR in both infants and adults. Babyfaceness also was correlated with an infant temperament that is a precursor of bolder behavior in childhood and adulthood, just as a broader infant FWHR was previously shown to be. These results call into question existing explanations for relationships between facial appearance and adult assertive or aggressive behavior. Previously, behavioral correlates of adult FWHR have been attributed to influences of pubertal testosterone, and correlates of adult babyfaceness have been attributed to compensation for undesirable stereotypes. Our findings indicate that the pre-natal developmental influences required to explain appearance–temperament relationships in infancy also should be considered as explanations for appearance–behavior relationships in adulthood. •FWHR in infancy predicts same personality qualities as FWHR and babyfaceness in adulthood.•Prenatal factors influence relationship of adult FWHR or babyfaceness to behavior.•Pinpointing the prenatal influences we found will elucidate impactful individual differences.