This study investigated the influence of guidance instruction and type of activity on parental guidance of young children's mathematics and scientific inquiry during cooking, games, and nature activities at home. Thirty families participated with their preschool-aged child; half were randomly assigned to an inquiry guidance instruction group and encouraged to support children's reasoning with open-ended prompts and questions. Families participated in activities for one month, some of which they audio-recorded. Families engaged in processes of comparing, predicting, evaluating and concluding more often after inquiry guidance instruction, and incorporated inquiry processes into all activity types. Mathematics was most frequently observed in games and cooking. The results suggest that parents can use inquiry guidance to support preschoolers' mathematics and scientific inquiry in a variety of activities performed at home. As children engage in inquiry-based learning during co-constructed activities with parents, they develop conceptual understanding of mathematics and scientific inquiry in a positive social context.