Background Maternal mental problems can interfere with the overall health and care of the child; some oral health studies have been trying to elucidate whether there is a relationship between maternal common mental disorders (CMD) and children's oral health status. Aim The aim was to investigate the influence of mothers that present CMD symptoms on their child's dental caries status. Design This cross‐sectional study was carried out in Pelotas with 530 mother/child (aged 2‐5 years old) dyads recruited from an epidemiological survey in August 2015 during the national vaccination campaign. A questionnaire was used to determine mother's CMD symptoms using the Self‐Reporting Questionnaire (SRQ‐20) and socioeconomic/demographic variables which were used for adjustment. Dental caries examination was performed. The outcome was obtained using the dmfs (decayed, missing, filled surfaces) index, based on OMS guidelines. Poisson regression with robust variance was used to estimate the risk ratio and 95% confidence interval (CI). Results Maternal CMD was positively associated with dental caries prevalence in children; the adjusted relative risk for every 1 SRQ‐20 score increase was 1.06 (95% CI 1.00‐1.12). Conclusions Our findings suggest that maternal mental health can impair children's oral health in relation to dental caries.