This study focused on the associations between timing and intensity of maternal employment in early childhood and the developmental outcomes of young Canadian children. We conducted a secondary analysis of data from the Canadian National Longitudinal Survey of Children and Youth using multiple linear regression. We tested the associations between mothers’ employment in the first four years of children’s lives and motor and social development of zero to 4-year-old-children and receptive language of 4 and 5-year-old-children. We also examined the association between working more than 20 h a week during the first 2 years of children’s lives and children’s outcomes. We found that mothers who returned to work when their children were between 0 and 4 years old had enhanced motor and social development in comparison to children of mothers who did not work during this time. Additionally, findings showed that relative to children of mothers who worked 20 h or less a week in the first 2 years of their children’s lives, in particular between 12 and 17 months, children of mothers who worked more than 20 h had lower receptive language scores at 4 and 5 years of age. These findings have implications for maternity and parental leave policy in Canada.