Emotion Regulation is one of the most widely studied variables in child development. However, it is a complex construct, and there are few validated instruments to evaluate children. The main goal of this study was to test the factorial structure of the Emotion Regulation Checklist (ERC) in two samples of Spanish children, one with 284 preschool children (48.3% girls; M = 4.38) and the other with 323 elementary school children (49.2% girls; M = 8.82). The ERC was completed by the children's teachers. Although this instrument has been validated in different cultural contexts, no studies have analyzed its psychometric properties in Spanish samples. An examination of the internal structure, using Exploratory Structural Equation Modeling (ESEM), revealed that the original two-factor model (Emotion Regulation and Lability/Negativity) fitted the elementary school children's data well; however, in the sample of preschool children, the factorial model showed poor goodness-of-fit indices. The reliability of the ERC subscales was .77 for ER and .88 for L/N in the preschool-aged sample, and .80 for ER and .77 for L/N in the sample of elementary school children. In addition, the relationship between the ERC and the Test of EmotionThis is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.