To evaluate the relationship between maternal cognitive performance and language and cognitive development of children between 24 and 36 months old of mothers who became pregnant in adolescence, in the city of Pelotas, Southern Brazil. This is a cross-sectional study nested in a cohort study with adolescent mothers who received prenatal care in the city’s public health system. To assess maternal cognitive performance, the Montreal Cognitive Assessment (MoCA) was used and Bayley Scales of Infant Development III (BSID-III) are used to assess children's language and cognition development. Data were analyzed using SPSS (Version 22.0) software. Pearson correlation, t-test, ANOVA and linear regression were performed. We evaluated 496 mother-child dyads. In the adjusted analysis, we found that children's language remained associated with maternal cognitive performance (p = .027, CI [0.0, 0.6]) and child’s gender (p < .001, CI [−7.2, −2.4]). Besides that children cognitive development remained associated with maternal cognitive performance (p = .008, CI [0.1, 0.6]) and child’s gender (p = .030, CI [−4.5, −0.2]). Our results suggest that poor maternal cognitive performance is associated with lower levels of children's language and cognitive development. The results contributing to early identification and intervention in children of mothers with poor cognitive performance at higher risk of negative developmental outcomes.