Background <p>Pediatric nurses operate in high-stakes environments characterized by emotional, cognitive, and physical demands. Excessive workload can undermine nurses’ ability to perform effectively, particularly when compounded by low self-efficacy. Core competencies such as clinical judgment, evidence-based practice, and communication are essential to pediatric nursing performance and are susceptible to the influence of psychological and environmental stressors.</p> Aim <p>This study aimed to examine the mediating role of self-efficacy in the relationship between workload and core competencies among pediatric nurses in Egyptian governmental hospitals.</p> Methods <p>A descriptive cross-sectional study was conducted from November 2024 to February 2025 with 198 pediatric nurses recruited from PICUs, NICUs, and pediatric wards using convenience sampling. Data were collected via self-administered questionnaires including the NASA Task Load Index (workload), General Self-Efficacy Scale, and the Core Competence Scale for Paediatric Specialist Nurses. Structural Equation Modeling (SEM) was used to assess direct and indirect effects.</p> Results <p>Nurses reported high workload (M = 63.79, SD = 10.21), low self-efficacy (M = 18.90, SD = 4.12), and low core competencies (M = 76.74, SD = 11.56). SEM results showed that workload negatively predicted self-efficacy (β = -0.285, <i>p</i> &lt; 0.001), and self-efficacy positively predicted core competencies (β = 2.186, <i>p</i> &lt; 0.001). Self-efficacy mediated the relationship between workload and core competencies, with a significant indirect effect (β = -0.624, <i>p</i> &lt; 0.001).</p> Conclusion <p>Self-efficacy acts as a psychological buffer against the negative effects of workload on professional performance. Enhancing nurses’ self-efficacy through targeted interventions may mitigate workload-related declines in core competencies and improve pediatric nursing care.</p> Clinical trial number <p>Not applicable.</p>