In a time when story-acting practices have gained increasing focus, little is known about the relations between family story acting and a child's interactions with the ideal models represented in stories. Drawing upon a cultural-historical perspective of play and development, this study is aimed at discovering how a child is able to interact with the conceptual models usually formed in stories such as "sharing" during family dramatic play. The case study reported in this paper related to a three-year-old child and the parents from Mainland China. A total 25.15 hours of video observations and interviews was collected over 16 family visits during 2 research periods. Findings suggested that a shared imaginary situation created during the co-construction of a play-world between a child and his/her parents had its importance in fostering the child's active explorations of the ideal descriptions of certain conceptual rules. A new interpretation of the play-world can be made considering the pretend form made in a play-world, which acts as a bridge between a child's real state of conceptual understanding and the ideal form of the concept described in a story-world.