Understanding children's inquiry often draws on exogenous understanding (i.e., scientists' inquiry, classroom expectations) without first understanding inquiry in children's everyday lives. In contrast, we examine young children's inquiry in their families to better understand their competent engagement in inquiry. Specifically, we develop an endogenous representation of inquiry as a members' phenomenon (IMP)--a representation formulated by participants in the course of their own activity. IMP highlights key moments in inquiry--beginning by orienting to inquiry, making progress by drawing on sensemaking resources, and orienting to ending inquiry. This representation also allows us to recognize evidence of young children's competence in managing interactional, affective, and epistemic challenges inherent in these key moments of inquiry; the diverse array of sensemaking resources through which children address those challenges; and a range of children's interests and concerns addressed within their inquiry. Furthermore, IMP provides a prism for reconceptualizing learning from learners' perspective: attending to how participants orient to a moment of inquiry, inquire together, and come to what counts to them as a satisfactory end to their inquiry. This representation of inquiry is an important step in basic learning sciences research and informative for the design of science and other domain learning environments.