Full-day kindergarten programs are expanding across North America, driven by a policy focus on early childhood development. These programs also affect parents' budget sets and may lead to changes in labour market outcomes. We exploit the unusual nature of Ontario's government school system to examine parents' labour supply response to a move from half-day to full-day kindergarten in Ontario's French – but not English – schools. We find no robust evidence of labour supply effects for fathers in two parent families, and only some limited and modest effects on mothers in two parent families. For single mothers, the point estimates suggest large and statistically significant effects on employment and hours of work, and in particular for working longer hours.