Key PointsQuestionAre government mask mandates associated with mask use among children in Alberta, Canada?FindingsThis cohort study of 939 children (age, 8-13 years) from August 2020 to June 2022 examined government masking mandates and child mask use; the odds of parents’ report of child mask use (often or always) was 18.3 times higher during the mask mandate compared with when there was no mandate, which was a significant difference. Each day without the mask mandate was associated with a 1.6% decrease in mask use.MeaningThe findings of this study suggest the importance of public health messaging and time since the mask mandate was lifted.