This study explores children's agency in shared book reading sessions with parents and its relation to family literacy characteristics, parents' literacy practices with children and children's print knowledge. Research participants were 142 Czech children, ages 3-6, and their parents. Parents rated their children's agency and the attributes of the home literacy environment in a questionnaire. The data shows that children in the sample exerted agency in shared book reading situations, some of them extensively. Out of the four components of agency, children's manifestations of volition in shared book reading appeared to be the most extensive, followed by asking questions, imitating reading and monitoring parents when they were reading to them. Overall, the results indicate that literacy-aimed activities, which the parents carry out with their children, relate to children's agency more than literacy qualities of the home, like the number of children's books, children's exposure to literacy, or parental education.