Objective Based on data from the Global Burden of Disease Study (GBD) 2021, this study aims to analyze trends in myocarditis among children and adolescents aged 0-19 years in China from 1990 to 2021 and predicts the disease burden trends from 2025 to 2050. Methods Data on incidence, prevalence, mortality, and disability-adjusted life year (DALY) of myocarditis in the Chinese population aged 0-19 years were extracted from the GBD 2021 database. Joinpoint regression was used to estimate annual percent change. The GBD comparative risk assessment framework was used to quantify four categories of risk factors: environmental/occupational risks, non-optimal temperature, high temperature, and low temperature. The ARIMA model was applied to forecast the disease burden trends from 2025 to 2050. Results From 1990 to 2021, the age-standardized prevalence rate of myocarditis in Chinese children and adolescents aged 0-19 years increased, while the age-standardized incidence rate, age-standardized DALY rate, and age-standardized mortality rate decreased. The overall disease burden in China exceeded the global average and that of regions with a middle socio-demographic index. Males had a higher disease burden than females. In 2021, non-optimal temperature and environmental/occupational risks collectively accounted for 66.4% of the disease burden, and DALYs and mortality attributable to high temperature showed an increasing trend. ARIMA model projections indicate that by 2050, the overall incidence of myocarditis will remain stable, whereas DALYs and mortality in the 5-9-year age group are expected to increase among Chinese children and adolescents aged 0-19 years. Conclusions In China, the age-standardized prevalence of myocarditis among children and adolescents aged 0-19 years increased continuously from 1990 to 2021, and males had higher values across all burden metrics than females. Projections for 2025-2050 suggest that the overall incidence of myocarditis will remain stable, whereas the disability and mortality burden in the 5-9-year age group will rise. An age- and sex-stratified prevention and control system should be established, and protection against extreme temperatures should be incorporated into the national strategy for children's cardiovascular health.