Purpose Serious games (SGs) have great potential for pediatric medical education. This study evaluated the efficacy of a SG in improving learner satisfaction, knowledge, and behavior. Materials and methods This was an investigator-blinded randomized controlled trial (RCT) comparing a SG against two controls: (i) adaptive tutorial (AT), and (ii) low-stimulus control (LSC). SG is a highly immersive role-playing game in a virtual hospital. AT delivers interactive web-based lessons. LSC is paper-based clinical practice guidelines. Metropolitan senior medical students at UNSW were eligible. A total of 154 enrolled and were block randomized to one intervention. Participants had access to one intervention for 8 weeks which taught pediatric acute asthma and seizure assessment and management. Satisfaction was assessed with Likert-scale responses to 5 statements and 2 free-text comments. Knowledge was assessed with 10 multiple-choice questions (MCQs). Clinical behavior was assessed during a 30-point simulated clinical management scenario (CMS). Primary analysis was performed on a modified intention-to-treat basis and compared: (1) SG vs. AT; and (2) SG vs. LSC. Results A total of 118 participants were included in the primary analysis (modified intention-to-treat model). No significant differences in MCQ results between the SG and control groups. SG group outperformed the LSC group in the CMS, with a moderate effect (score out of 30: 20.8 (3.2) vs. 18.7 (3.2), respectively, d = 0.65 (0.2–1.1), p = 0.005). No statistically significant difference between SG and AT groups in the CMS (score: 20.8 (3.2) vs. 19.8 (3.1), respectively, d = 0.31 (–0.1 to 0.8), p = 0.18). A sensitivity analysis (per-protocol model) was performed with similar outcomes. Conclusions This is the first investigator-blinded RCT assessing the efficacy of a highly immersive SG on learner attitudes, knowledge acquisition, and performance in simulated pediatric clinical scenarios. The SG demonstrated improved translation of knowledge to a simulated clinical environment, particularly compared to LSC. SGs show promise in pediatric medical education.