ImportanceInjuries from firearms and motor vehicle crashes (MVCs) are the leading causes of death among US children and youths aged 0 to 19 years. Examining the intersections of age group, sex, race, and ethnicity is essential to focus prevention efforts.ObjectiveTo examine firearm and motor vehicle fatality rates by population subgroups and analyze changes over time.Design, Setting, ParticipantsThis cross-sectional study of firearm and MVC fatalities among US children and youths aged 0 to 19 years from the Centers for Disease Control and Prevention Web-Based Injury Statistics and Query Reporting System from 2011 to 2021. Participants included American Indian and Alaska Native; Asian, Hawaiian Native, and Pacific Islander; Black; Hispanic; and White youths. Data analysis was conducted from July 2023 to May 2024.ExposureFirearm or MVC fatality.Main Outcome MeasuresFirearm and MVC fatality rates by year and over time, as measured by the Joinpoint regression annual percent change (APC).ResultsFrom 2011 to 2021 there were 35 684 firearm and 40 735 MVC fatalities among US youths aged 0 to 19 years. For firearm fatalities, there were 21 332 homicides (59.8%), 12 113 suicides (33.9%), 1359 unintentional shootings (3.8%), 277 by legal enforcement (0.8%), and 603 from unknown intents (1.6%). When considering the intersections of age group, sex, race, and ethnicity, for firearm homicides among youths aged 15 to 19 years, the APCs were similar for Black (21.8%) and Hispanic (22.2%) males from 2018 to 2021, although with different peak rates (104.22 per 100 000 individuals and 17.80 per 100 000 individuals, respectively, in 2021). Black females aged 15 to 19 years demonstrated a dramatic APC increase of 40.7% from 2019 to 2021 (peak rate, 14.07 per 100 000 individuals). For firearm suicide in youths aged 10 to 19 years by sex, Black females had the greatest APC increase of 22.0% from 2016 to 2021. For MVC fatalities, the highest APC increase of 24.9% occurred among American Indian and Alaska Native females aged 15 to 19 years from 2018 to 2021. The highest MVC fatality rates occurred in 2021 among American Indian and Alaska Native males (38.16 per 100 000 individuals) and females (29.31 per 100 000 individuals) aged 15 to 19 years.Conclusions and RelevanceIn this cross-sectional study, US youths aged 0 to 19 years experienced important disparities in firearm and MVC fatality rates and increases over time when considering the intersectionality by age group, sex, race, and ethnicity. These findings suggest that a multipronged strategy focused on individual, community, and policy level approaches for specific high-risk groups for each injury mechanism is necessary to address these leading causes of death in US youths.