To assess the impact of the COVID-19 pandemic on stress and mental health using a baseline measure, we designed an opportunity study in which dyads of parents (N=133, 74% mothers) and children (59% girls, 11-12 y/o) from a research project conducted in 2019 (baseline) were recontacted for data collection during the onset of the pandemic in April 2020 (T2) in Canada. Dyads completed self-report measures of perceived stress, anxiety and emotion regulation (ER) strategies. Mixed ANOVAs revealed an increase in parents’ stress (p<.001, n²p=.27) and state anxiety (p<.001, n²p=.16) compared to baseline, but not in their children (resp. p=.19, p=0.28). Dyads’ anxiety sensitivity remained unchanged (resp. p=.03, p=.28). Parents showed similar use of ER strategies (p=.22) while children showed similar use of cognitive reappraisal (p=.32) but less emotional suppression (p=.005, n²p=.06) and co-rumination (p<.001, n²p=.18) at T2 compared to baseline. Finally, parental and children scores on mental health measures were not correlated at either time. Our results suggest that during the onset of the pandemic, parents and children responded differently in terms of stress and mental health and used different emotion regulation strategies.