This study explores preschool children's mathematizing in everyday block play activities. Building on an ethnomethodological and multimodal conversation analytic framework, we explore how geometry (i.e. spatiality, shape, and symmetry) is actualized in children's verbal and embodied interaction with their peers, pedagogues, and material environment. The selected data are drawn from a video ethnographic study in a Swedish preschool in which a boy and a girl play with a magnetic construction toy. The results of the study demonstrate how the participants orient to spatial locations, properties, dimensions, orientations, transformations, and shapes as they build a house. The children are shown to rely upon verbal and embodied resources such as deictics (e.g. here, there, these) and pointing gestures as geometrical aspects are actualized in their interaction. The study contributes with knowledge on preschool children's everyday mathematizing, in particular, children's appropriation of geometric discourse as it emerges in the unfolding flow of interaction.