Emotion regulation is one of the important skills helping children and parents to deal with stressful conditions within the family context during the pandemic. We aimed to investigate whether mothers' emotion regulation strategies before COVID-19 and their COVID-19-related anxiety would predict children's sadness regulation during the pandemic with a longitudinal design. A total of 310 children, aged 7-17, and their mothers from Türkiye participated in the current study. Maternal reappraisal and suppression did not predict children's sadness regulation skills. Maternal COVID-19-related anxiety positively predicted children's inhibition during the pandemic over and above maternal emotion regulation skills and children's pre-pandemic sadness regulation skills. Age also predicted children's inhibition levels, such that as children got older, their inhibition levels increased. Findings highlight the importance of the emotional climate of the family environment during the pandemic for emotional development in the Turkish context.