Affective flexibility (AF) is the ability to alternate between processing emotional and non-emotional information. This hot executive function has been understudied during early development. The first aim of our investigation was to generate preliminary construct validity evidence for a new measure of AF: the Emotional Flexible Item Selection Task (EM-FIST). Second, to investigate if AF represented a better predictor of preschoolers' emotion regulation (ER) compared to, cognitive flexibility (CF). Preschoolers (N = 56; 48.2% girls) completed AF and CF measures (also working memory and inhibitory control). ER was measured through maternal report. We found evidence of EM-FIST's validity, as an appropriate measure of AF for preschoolers, by showing that it is related to cool executive functions' measures and to children's ER. Both AF and maternal level of education predicted children's ER while CF did not. Our investigation highlights a stronger relation between ER and AF in preschoolers than with CF.