Many studies have demonstrated a positive association between familial activities (e.g. reading to the child) and children's development in different domains. It is also well-known that social and ethnic differences exist regarding the frequencies of such activities. However, the mechanism behind these differences is less clear. This article analyses the role of parents' cultural capital as a mediating factor between families' social and ethnic background and the frequency of stimulating familial activities in early childhood. Using the data from the German longitudinal study "Preschool Education and Educational Careers among Migrant Children", it is shown that parents' cultural capital completely mediates the effect of mother's education and part of the ethnic origin effect. Additional longitudinal analyses reveal that the influence of parents' cultural capital changes over time and is most pronounced at the earliest measurement.