"Research Findings": Empathy is a relevant component of social interactions that can be observed from early childhood. Validated tests for young children are still scarce. This study has two goals: (1) to validate the modified two-factor version of the Interpersonal Reactivity Index (IRI) in Spanish children between the ages of 3 and 8; and (2) to explore the mediational role of emotion regulation in the relationship between empathy and social competence. Teachers of 118 Spanish children from 3 to 8 years old completed the IRI, the Emotion Regulation Checklist, and a scale of Social Competence. The results confirmed the two-factor structure of the modified version of the IRI and showed acceptable psychometric properties in the sample, acceptable to good reliability, and adequate construct validity. The mediational model revealed that the relationship between Empathy and Social Competence was mediated by Emotion Regulation, partially in the case of Empathic Concern and fully in the case of Perspective Taking.. "Practice or Policy": Our results highlight the relevance of emotion regulation in childhood and the need to address the multidimensional nature of empathy. This knowledge can contribute to the understanding and promotion of socio-emotional development in childhood.