Canada legalized cannabis in October 2018 but initially prohibited the sale of edibles (eg, prepackaged candies). Starting in January 2020, some provinces permitted the sale of commercial cannabis edibles. The association of legalizing cannabis edibles with unintentional pediatric poisonings is uncertain. To evaluate changes in proportions of all-cause hospitalizations for poisoning due to cannabis in children during 3 legalization policy periods in Canada's 4 most populous provinces (including 3.4 million children aged 0-9 years). This repeated cross-sectional study included all hospitalizations in children aged 0 to 9 years in Ontario, Alberta, British Columbia, and Quebec between January 1, 2015, and September 30, 2021. Prelegalization (January 2015 to September 2018); period 1, in which dried flower only was legalized in all provinces (October 2018 to December 2019); and period 2, in which edibles were legalized in 3 provinces (exposed provinces) and restricted in 1 province (control province) (January 2020 to September 2021). The primary outcome was the proportion of hospitalizations due to cannabis poisoning out of all-cause poisoning hospitalizations. Data analysis was performed using descriptive statistics and Poisson regression models. During the 7-year study period, there were 581 pediatric hospitalizations for cannabis poisoning (313 [53.9%] boys; 268 [46.1%] girls; mean [SD] age, 3.6 [2.5] years) and 4406 hospitalizations for all-cause poisonings. Of all-cause poisoning hospitalizations, the rate per 1000 due to cannabis poisoning before legalization was 57.42 in the exposed provinces and 38.50 in the control province. During period 1, the rate per 1000 poisoning hospitalizations increased to 149.71 in the exposed provinces (incidence rate ratio [IRR], 2.55; 95% CI, 1.88-3.46) and to 117.52 in the control province (IRR, 3.05; 95% CI, 1.82-5.11). During period 2, the rate per 1000 poisoning hospitalizations due to cannabis more than doubled to 318.04 in the exposed provinces (IRR, 2.16; 95% CI, 1.68-2.80) but remained similar at 137.93 in the control province (IRR, 1.18; 95% CI, 0.71-1.97). This cross-sectional study found that following cannabis legalization, provinces that permitted edible cannabis sales experienced much larger increases in hospitalizations for unintentional pediatric poisonings than the province that prohibited cannabis edibles. In provinces with legal edibles, approximately one-third of pediatric hospitalizations for poisonings were due to cannabis. These findings suggest that restricting the sale of legal commercial edibles may be key to preventing pediatric poisonings after recreational cannabis legalization.