The corpus callosum connects and integrates the activities of the left and right cerebral hemispheresandhas been reported to show the most noticeable growth from infancy to early adulthood. The goal of the present study was to examine the longitudinal effect of maternal parenting and attachment to their children on the growth of the children’s corpus callosum. The participants were 11 normal children and their mothers. Magnetic resonance imaging and the diffusion tensor imaging scanning were performed on the children at 2 and 6 years of age. The increase in corpus callosum fractional anisotropy was obtained by calculating the difference between images taken at 2 and 6 years old. The attachment of the mother to the child was assessed using Q-sort when the children were 1 year of age, and maternal affective parenting was rated through a self-reported scale by the mother when their child was 3 years of age. The increase in corpus callosum fractional anisotropy from 2 to 6 years of age was affected by attachment and maternal affective parenting. The weight of attributed to the effect of maternal affective parenting on the increase in corpus callosum fractional anisotropy was greater than that of attachment. Thus, we conclude that everyday life experience, particularly the affective aspect of maternal caring, is the most powerful factor affecting the development of the brain at an early age.