IMPORTANCE: COVID-19 vaccinations are recommended for minors. Surveys indicate lower vaccine acceptance by some immigrant and refugee groups. OBJECTIVE: To identify characteristics in immigrant, refugee, and nonimmigrant minors associated with vaccination. DESIGN, SETTING, AND PARTICIPANTS: This retrospective cohort study used linked, population-based demographic and health care data from Ontario, Canada, including all children aged 4 to 17 years registered for universal health insurance on January 1, 2021, across 2 distinct campaigns: for adolescents (ages 12-17 years), starting May 23, 2021, and for children (ages 5-11 years), starting November 25, 2021, through April 24, 2022. Data were analyzed from May 9 to August 2, 2022. EXPOSURES: Immigrant or refugee status and immigration characteristics (recency, category, region of origin, and generation). MAIN OUTCOMES AND MEASURES: Outcomes of interest were crude rates of COVID-19 vaccination (defined as ≥1 vaccination for children and ≥2 vaccinations for adolescents) and adjusted odds ratios (aORs) with 95% CIs for vaccination, adjusted for clinical, sociodemographic, and health system factors. RESULTS: The total cohort included 2.2 million children and adolescents, with 1 098 749 children (mean [SD] age, 7.06 [2.00] years; 563 388 [51.3%] males) and 1 142 429 adolescents (mean [SD] age, 14.00 [1.99] years; 586 617 [51.3%] males). Among children, 53 090 (4.8%) were first-generation and 256 886 (23.4%) were second-generation immigrants or refugees; among adolescents, 104 975 (9.2%) were first-generation and 221 981 (19.4%) were second-generation immigrants or refugees, most being economic or family-class immigrants. Immigrants, particularly refugees, were more likely to live in neighborhoods with highest material deprivation (first-generation immigrants: 18.6% of children and 20.2% of adolescents; first-generation refugees: 46.4% of children and 46.3% of adolescents; nonimmigrants: 18.5% of children and 17.2% of adolescents) and COVID-19 risk (first-generation immigrants; 20.0% of children and 20.5% of adolescents; first-generation refugees: 9.4% of children and 12.6% of adolescents; nonimmigrants: 6.9% of children and 6.8% of adolescents). Vaccination rates (53.1% in children and 79.2% in adolescents) were negatively associated with material deprivation. In both age groups, odds for vaccination were higher in immigrants (children: aOR, 1.30; 95% CI, 1.27-1.33; adolescents: aOR, 1.10; 95% CI, 1.08-1.12) but lower in refugees (children: aOR, 0.34; 95% CI, 0.33-0.36; adolescents: aOR, 0.88; 95% CI, 0.84-0.91) compared with nonimmigrants. In immigrant- and refugee-only models stratified by generation, region of origin was associated with uptake, compared with the overall rate, with the lowest odds observed in immigrants and refugees from Eastern Europe (children: aOR, 0.40; 95% CI, 0.35-0.46; adolescents: aOR, 0.41; 95% CI, 0.38-0.43) and Central Africa (children: aOR, 0.24; 95% CI, 0.16-0.35; adolescents: aOR, 0.51,CI: 0.45-0.59) and the highest odds observed in immigrants and refugees from Southeast Asia (children: aOR, 2.68; 95% CI, 2.47-2.92; adolescents aOR, 4.42; 95% CI, 4.10-4.77). Adjusted odds of vaccination among immigrants and refugees from regions with lowest vaccine coverage were similar across generations. CONCLUSIONS AND RELEVANCE: In this cohort study using a population-based sample in Canada, nonrefugee immigrants had higher vaccine coverage than nonimmigrants. Substantial heterogeneity by region of origin and lower vaccination coverage in refugees persisted across generations. These findings suggest that vaccine campaigns need precision public health approaches targeting specific barriers in identified, undervaccinated subgroups.