To slow down the spread of the COVID-19 virus, schools around the world were closed in early 2020, transferring children's scholastic activities to the homes and imposing a massive burden on parents and school-age children. Using data of a 21-day diary study conducted between March and April 2020 in Germany, this work examined whether (a) distance learning and (b) parents' involvement therein were associated with negative parent--child interactions and affective well-being of parents and children, over and above the effect of daily stressors. Participants were 562 parents (489 mothers, M[subscript age] = 42.79, SD[subscript age] = 6.12, range = 25-63) most of whom were married (n = 382, 68.0%). They responded to the daily items with respect to the youngest child living in their household (M[subscript age] = 9.74, SD[subscript age] = 2.81, range = 6-19). On days when children were working on school tasks, parents reported more negative parent-child interactions as well as lower parental and child positive affect and higher child negative affect, but not higher parental negative affect. Moreover, days when parents were more heavily involved in learning (i.e., when children worked less independently) were days with more negative parent-child interactions, lower parental and child positive affect, and higher parental and child negative affect. Negative parent-child interactions were linked to lower affective well-being of parents and children, and partially accounted for the relation among daily stressors and affective well-being. The present work highlights the need for measures to better support school-age children and their parents during distance learning.