This study examines the relationships between temperament traits (negative affectivity, extraversion and effortful control) and children’s externalized and internalized behavioral problems. The sample was composed of 424 children from the ages of 3–6 years old (60% male). Use of a hierarchical regression analysis revealed direct and interactive effects. Specifically, reactive temperamental traits were found to predict behavioral problems in children: negative affect tended to increase externalizing problems, and extraversion tended to decrease internalizing problems. The regulative temperament trait (“effortful control”) negatively predicted both internalizing and externalizing problems. To explore moderating effects, post‐hoc analyses were conducted using the Johnson–Neyman technique with Hayes’s PROCESS. Our analyses revealed that high levels of negative affect (characterized in our study by a higher load of anger or frustration than of fear or sadness) makes a significant and strong contribution to internalizing problems when effortful control reaches its highest levels. Thus, our results endure the protective role of extraversion as preventing the emergence of internalizing problems, and the protective role of effortful control as preventing the emergence of both, internalizing and externalizing, problems. The results also alert to the potential risk of a combination between high levels of effortful control and high levels of negative affect. Overall findings are discussed with regard to previous and future research.