Background <p>Nursing is a demanding profession associated with elevated levels of occupational stress, which can negatively affect nurses’ mental well-being, job satisfaction, and capacity for caring behaviour. Paediatric and psychiatric nurses face distinct stressors related to their work environments and patient populations. This study aimed to compare occupational stress, mental well-being, and caring behaviours among nurses working in paediatric and psychiatric settings in Slovenia, where limited research has examined how work environment characteristics influence nurses’ psychological well-being.</p> Methods <p>A cross-sectional single-centre study using convenience sampling was conducted between September 2024 and February 2025 in a public teaching hospital in Slovenia. A total of 105 nurses (66 psychiatric, 39 paediatric) completed a structured questionnaire including the Warwick-Edinburgh Mental Well-being Scale, Nurses’ Stress Scale, and Caring Dimensions Inventory. Due to non-normal data distribution, non-parametric tests (Mann–Whitney U and Kruskal–Wallis) were used alongside linear regression analysis to examine group differences and associations between variables. The study adhered to the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) statement.</p> Results <p>No statistically significant differences were found in stress levels or caring behaviours between paediatric and psychiatric nurses. However, psychiatric nurses reported higher mental well-being, though the difference was non-significant (<i>p</i> = 0.050). Significant associations were observed between mental well-being and self-rated general health (<i>p</i> = 0.008), education level (<i>p</i> = 0.011), and marital status (<i>p</i> = 0.048). Linear regression indicated that more years of work experience were associated with slightly lower stress levels (<i>p</i> = 0.013), although the explained variance was modest (R² = 0.059).</p> Conclusions <p>The findings suggest that individual and contextual factors, such as perceived health, education, and marital status, may have a stronger influence on nurses’ mental well-being than the specific clinical setting. While stress and caring behaviours were relatively stable across groups, targeted strategies to support nurses’ psychological health should consider broader personal and occupational characteristics. Understanding how demographic and psychosocial variables affect nurses’ mental well-being is essential for developing effective interventions. Promoting resilience and mental health in nursing requires a multidimensional approach that addresses both workplace factors and individual circumstances.</p> Clinical trial number <p>Not applicable.</p>