One possible source of variation in children's mathematical abilities upon entry to school may be the social support of early number skills children receive in the home. In the present study, we explored parental support of preschoolers' counting in the context of an everyday activity and whether parental ability to provide aid is influenced by the presence of a school-age sibling. Thirty-five middle-class families (19 dyads and 16 triads) were videotaped as they played a board game. While there were many similarities across the two conditions in the amount and type of support parents provided, those playing the game with only a preschooler were more likely to use their turns as teaching opportunities, and to adjust their aid according to their preschoolers' mathematical abilities. Potential factors influencing these differences as well implications for research and practice are discussed.