Parents play a pivotal role in introducing their children to science, but little is known about the nature of an early science-related home learning environment. This study examines different aspects of the home learning environment and their associations with children's science knowledge. Mediation analyses of a sample of 257 five-year-old preschool children and their parents show that (1) parental engagement in science-related learning activities with their children is associated with children's science knowledge, (2) structural family characteristics as well as parental interest in science are associated with the frequency of these activities, and (3) associations of structural family characteristics and parental interest in science with children's knowledge are mediated by science-related activities. The results emphasize the important role of parents in children's early science education.