This measurement validity study assesses the Hughes and Chen (1997) Multidimensional Scale of Race Socialization in an early childhood sample to examine when ethnic-racial socialization (ERS) strategies emerge and the degree to which they are employed with young children. We administered the Multidimensional Scale among a sample of 407 African American and Latinx families. Data were collected across four waves (child ages 2.5-7.5 years). Longitudinal, multigroup confirmatory factor analyses were modeled to test (a) factorial validity of the extant measure in a novel group, (b) equivalence of measuring ERS across age, gender, and ethnicity, and (c) latent means across the sample. The two-factor model was validated in this early childhood sample and measured invariantly across all waves and groups. Latent means of cultural socialization and preparation for bias steadily increased across early childhood with noteworthy differences in effect sizes (.58-.75, respectively) between the second and third assessments when the majority of children entered kindergarten. Latent means did not differ for caregivers on account of child gender. African American caregivers reported greater messaging of cultural socialization (ES range: .44-1.55) than Latinx caregivers, and also reported greater preparation for bias than their Latinx peers but only at school entry (ES = .66). This study provides evidence that ERS strategies commonly used with older children emerge very early on in family experiences and supports the notion that the transition to kindergarten marks a notable ecological shift for ethnic minority children. (PsycInfo Database Record (c) 2022 APA, all rights reserved).