Racism is a determinant of individual and offspring health. Accelerated telomere shortening, an indicator of cellular aging, is a potential mechanism through which parental experience of racism could affect offspring. Here we longitudinally evaluated the relationship between maternal lifetime experience of an ethnically-motivated verbal or physical attack, as reported in pregnancy, with offspring telomere length in 4.5-year-old children. We also explored the potential association between positive feelings about one’s culture and offspring telomere length. Data come from a nationally representative, multi-ethnic birth cohort in Aotearoa New Zealand (NZ) (Māori N = 417, Pacific N = 364, Asian N = 381). In models adjusting for covariates, including socioeconomic status and health status, Māori mothers who experienced an ethnically-motivated physical attack had children with significantly shorter telomere length than children of Māori mothers who did not report an attack (B = − 0.20, p = 0.01). Conversely, Māori mothers who had positive feelings about their culture had offspring with significantly longer telomeres (B = 0.25, p = 0.02). Our results suggest that ethnicity-based health inequities are shaped by racism, with impacts for clinical care and policy. Future research should also evaluate the potential protective effects of positive cultural identity.