Background: Type 1 diabetes demands extensive self-care including multiple daily insulin injections, several finger-pricks daily for blood glucose testing, and venipuncture when attending the outpatient clinic. Simulation-based education serves as a link between classroom learning and clinical practice. It aids nursing competency before working with neonates in a real-life environment, hence improving the quality of care and ensuring neonates' safety. This study aimed to evaluate the impact of simulation-based intervention on nurses' performance regarding insulin self-injection for diabetic children. Method: A quasi-experimental research design was used. Setting: The study was conducted at Pediatric Diabetes inpatient and outpatient Clinics at Sohag University Hospital. Subjects: A convenient sample of all nurses (50) who are working in the previously mentioned setting. Tools for data collection: (1) an insulin self-injection questionnaire sheet and (2) an observational checklist were used to collect data. Results:  Between the knowledge and practice of the nurses under study, there was a very statistically significant difference. Before implementing the simulation-based intervention, the study found that three-quarters of the nurses had inadequate knowledge and three-fifths had inadequate practice with insulin self-injection for children with diabetes. Following the implementation of simulation-based intervention, the majority of the nurses in the study demonstrated a satisfactory level of practice and a good level of knowledge. After the simulation-based intervention, nurses' performance improved and changed in a highly statistically significant way compared to before. Conclusion: According to the current study's findings, nurses' performance in administering insulin to children with diabetes improved when they participated in a simulation-based intervention. Recommendations: The study recommended that nurses be trained in insulin self-injection for children with diabetes using a simulation-based intervention.