In Japan, gendered division of labor has been the norm. Therefore, it is predominantly the mothers who take care of their infants. We confirmed this trend in our survey with the question: “who is the child’s main caregiver during the day?”. In the first survey when the child was aged 6 months, we confirmed that 91% of the 2001 cohort and 95% of the 2010 cohort identified ‘mother’ as the main caregiver. We reanalyzed the data with the restricted sample, but we did not see differences from the original analyses.