The current 3-generation (N = 204 families), 3-year longitudinal study examined the intergenerational transmission of cultural socialization among Mexican-origin young mothers and their own mothers (i.e., children's grandmothers) and, in turn, whether young mothers' cultural socialization informed their children's developmental competencies (i.e., interactive play with peers, receptive language, and internalizing and externalizing problem behavior) one year later. Results indicated that mediation was significant, such that grandmother-mother cultural socialization, when children were 3 years old, informed greater mother-child cultural socialization when children were 4 years old, which, in turn, informed children's greater receptive language and interactive play with peers when children were 5 years old. Findings highlight the importance of intergenerational cultural socialization on young children's developmental competencies. (PsycINFO Database Record (c) 2020 APA, all rights reserved).