Cardiorespiratory fitness (CRF), commonly assessed using maximal oxygen uptake (VO₂max), is an important health marker in children and adolescents. We compared the effects of different exercise types and examined dose-response associations with CRF. PubMed, Embase, the Cochrane Library, and Web of Science were searched from inception to June 2026 for randomized controlled trials involving participants younger than 18 years. All analyses were conducted after the final search. Interventions were classified as high-intensity interval training (HIIT), sprint interval training (SIT), high-intensity aerobic exercise (HAE), moderate-intensity aerobic exercise (MAE), combined exercise (CE), or resistance exercise (RE). We performed an arm-based Bayesian multilevel random-effects network meta-analysis and Bayesian meta-regression. Fifty-two trials involving 4, 308 participants were included. Compared with the control group, HIIT had the largest estimated improvement in CRF (mean difference [MD] = 2.50, 95% credible interval [CrI]: 1.46 to 3.51), followed by SIT (MD = 2.05, 95% CrI: 0.85 to 3.22), CE (MD = 1.95, 95% CrI: 0.87 to 2.98), and HAE (MD = 1.25, 95% CrI: 0.09 to 2.41). The intervals for MAE and RE included the null value. Dose-response analyses showed the highest posterior mean effects around 1,100 METy-min/week, 40 min/session, and a METy-based intensity of approximately 8.5 METy, although the weekly-dose estimate remained imprecise. Exercise interventions were associated with improved CRF in children and adolescents, with HIIT and SIT ranking most favorably. Study-level analyses suggested favorable patterns around 1,100 METy-min/week, 40 min/session, and 8.5 METy, although these should not be considered precise optimal prescriptions.