For decades, the notion has persisted in developed countries that exclusive care by the mothers is best for the development of children up to 3 years of age. To examine the veracity of this "myth of the first three years" in Japan, we examined the effects of childcare facility use for children younger than 3 years on their development using the cohorts of the Longitudinal Survey of Newborns in the 21st Century conducted in Japan. Of the 47,015 respondents to the survey, we studied the children of 5,508 mothers with university/professional education to evaluate the relationships between primary early (< 2.5 years) childcare providers during weekday daytime hours and specific development indices for the ages of 2.5, 5.5, and 8 years. At the age of 2.5 and 5.5 years, children attending childcare facilities were judged as having more advanced developmental behaviors by their parents, such as being able to compose a two-word sentence (adjusted odds ratio [aOR]: 0.22) or to express emotions (aOR: 0.81), compared with those cared for by mothers. However, at the age of 8 years, children who attended childcare facilities as infants < 2.5 years showed more aggressive behavior in interrupting people (aOR: 1.20) and causing disturbances in public (aOR: 1.26) than those cared for by mothers (after adjustment for numerous child and parental factors). Although these results are generally consistent with previous studies, issues potentially involved with problem behavior such as quality of childcare require further investigation, as does the case of children of mothers with more modest educational attainment.
Keywords: child development; childcare; educational attainment; problem behavior; “myth of the first three years”.