Physiological indicators like heart rate (HR) and its variability (HRV) from ECG (electrocardiograms), and frontal lobe alpha power asymmetry (AA) and frontoparietal connectivity from EEG (electroencephalograms), can elucidate the role of the nervous system and other visceral organs and their effects on behavioral measures of cognitive and emotional self-regulation. Knowledge of the intergenerational transmission of cardiac and cerebral physiology can provide insight as to the developmental patterns of the organization and stabilization of these physiological processes in children and their mothers. The current study addresses a key question: Is there a developmental shift from 3-9 years of age in the overall pattern of EEG and ECG similarity between children and their mothers? The hypothesis was that there would be increasing child-mother similarity with age. EEG and ECG physiology was examined during a resting-state baseline period, during completion of cognitive tasks, and as baseline-to-task changes in EEG AA and frontoparietal coherence, and ECG HR and HRV in children and their mothers. A socioeconomically diverse longitudinal sample of 171 mothers with their children at ages 3, 6, and 9 years completed questionnaires and laboratory visits. Results indicated that there was some evidence to suggest the presence of mother-child similarity. Twenty of the seventy-two estimated intraclass correlations were significant. Furthermore, of the 20 significant correlations overall, none were present at child age 3 years, 6 were significant at child age 6 years, and 14 were significant at child age 9 years. Thus, overall, there was evidence that by age 6 years, child-mother similarity in physiological indicators of SR had begun to emerge. Additionally, consistent with the study hypothesis, there was some evidence of a pattern of increasing similarity for certain physiological indicators. Of the 72 estimated age-difference Fisher tests for increasing similarity, 17 were significant and in the hypothesized direction. The greatest number were seen during the task condition for ages 6 and 9, and particularly for the frontoparietal EEG variables. Findings are interpreted in light of social learning and behavioral genetics theories.