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 examine parents’ labour supply response to the move from half-day to full-day kindergarten in Ontario’s French schools well before the same change was made in English schools. We find no robust evidence of labour supply effects for fathers in two-parent families and only some limited and modest effects for mothers in two-parent families. For single mothers, the estimates suggest large and statistically significant effects on employment and hours of work, in particular for working longer hours.