In the context of rapid urbanization, the construction of child-friendly public spaces has become an important topic in urban design and planning. As small-scale green open spaces situated within residential areas, pocket parks play a significant role in enhancing community livability and enriching children’s everyday outdoor experiences. This study, based on the Mosaic Approach proposed by British scholars Alison Clark and Peter Moss, employs a multi-dimensional participatory methodology integrating children’s drawings, semi-structured interviews, and behavioral observation to explore the spatial perception, behavioral preferences, and emotional expressions of children aged 6–12 toward pocket parks. A conceptual framework of “children’s spatial perception–emotional cognition–behavioral preference” was constructed. Through content and thematic analysis of 30 children’s drawings and corresponding interviews, six core themes were identified: biophilic attachment, exploration and play experience, social belonging, safety and control, rest and comfort, and spatial cognition and accessibility. The findings indicate that children’s perceptions of pocket parks exhibit a progressive structure from sensory and emotional experience to behavioral interaction and cognitive understanding. Accordingly, six child-centered design strategies are proposed, emphasizing multi-sensory natural experiences, exploratory play spaces, inclusive social areas, perceivable safety, comfortable resting zones, and clear spatial organization. The study verifies the scientific validity and applicability of the Mosaic Approach in children’s spatial research and provides theoretical support and practical guidance for the design of micro-scale, child-friendly urban spaces. It advocates a paradigm shift from “designing for children” to “co-creating with children,” promoting more inclusive, human-centered, and participatory urban environments.