Emotion comprehension (EC), theory of mind (ToM), and language are particularly important aspects of child development. In recent years, there has been increasing interest in understanding how these three variables are related to preschool children. However, results have been contradictory, and it is not clear how EC, ToM, and language are associated. The aim of this study was to analyze the relationships among EC, ToM, and language through a longitudinal study. Participants were 105 children (49 girls and 56 boys). EC, ToM, and language skills were assessed when children were 3, 4, and 5 years old. The cross-lagged model confirmed that EC preceded ToM in time. The half-longitudinal model showed that linguistic skills at 4 years old mediated the relationship between EC at 3 years old and ToM at 5 years old. These findings provide important insights into the complex relationships among EC, ToM, and language. Developmental, educational, and clinical implications of the results are discussed.