Objective: This study investigates the effects of paternal involvement on the frequency of gender-incongruent activities in children's play at age 2. Background: Recent research suggests that paternal involvement is associated with more gender egalitarian attitudes in children and a more egalitarian distribution of housework tasks between sons and daughters. Although previous studies have tested the effects of paternal involvement on teenage children, the process of internalization of gender norms and roles in early childhood has not yet been investigated. Method: Analyses are based on the French Elfe cohort with information at age 2 for 11,564 children born in 2011. Multivariate linear and multinomial logistic regression models were run separately for sons and daughters. Results: Paternal involvement in early childhood was associated with more frequent gender-incongruent activities in boys' but not in girls' play at age 2. The effect of paternal involvement further varied depending on the type of involvement: involvement in housework tasks and childcare was associated with more gender-incongruent activities for sons but paternal participation in children's play increased the frequency of activities gender-typed as masculine, independently of the child's sex. Conclusion: Paternal involvement in housework and childcare in early childhood shapes gender-typed activities in toddlers' play for sons but not for daughters. It contributes to "undoing gender" in play activities for boys and, in doing so, narrows the gender gap in children's play.