Preschool programs for socially vulnerable children are believed to affect school readiness and language development but infrequently include follow-up to adolescence; observational measurement of receptive vocabulary is rare. The purpose of this longitudinal cohort study (55 children and 41 parents) was to report the trajectory of receptive vocabulary development for socially vulnerable children of diverse ethnicities (Indigenous, other Canadian-born, and Immigrant) who participated in a two-generation preschool program. English receptive vocabulary scores were measured at 5-time points: (a) program intake, (b) program exit, (c) age 7 years, (d) age 10 years, and (e) adolescence, using the Peabody Picture Vocabulary Test - Third Edition (PPVT-III). For all children, PPVT-III scores increased the most between program intake and exit and positive changes were sustained until adolescence. When the sample was examined by gender, PPVT-III scores were higher for boys than girls at all time points. When the sample was examined by ethnicity, other Canadian-born children scored higher than Indigenous and Immigrant children at all time points. Immigrant children scored lowest until age 7 years, and at age 10 years and adolescence scored higher than Indigenous children. Using mixed-effects modeling, PPVT-III scores increased when English was the primary language spoken at home at intake. PPVT-III scores increased slightly as caregiver age and caregiver Adverse Childhood Experiences score increased. PPVT-III scores were lower for Immigrant girls and Indigenous boys than other sub-groups of children. Differential effects of the two-generation preschool program by gender and ethnicity suggest tailoring programming to increase equitability of receptive vocabulary development for immigrant girls and Indigenous boys. Children with intergenerational adversity may require additional support.