In the context of the decline in working-age population and exhaustion of demographic dividend in China, how to increase the supply of labor has become an issue critical to economic development. Optimizing preschool education system and enhancing the accessibility of high-quality and low-cost pre-primary schooling help free married women from childcare, boost their labor force participation, and thus, augment the supply of labor. This study discovers that the labor force participation rate of women who enroll all their preschool-age children in kindergartens is 1.32 times that of those who do not do so; and that for working women, preschool attendance of all their kids can increase their working time by four hours per week. After classifying the sample according to the level of household income and type of Hukou (registered permanent residence), it finds that child preschool attendance can more significantly raise the employment probability of women from high-income families and more prominently increase working hours of those with rural Hukou.