To all kinds of design, the negotiation between the expression of designers’ idea and the representation of users’ desire is a typical internal tension of design. Particularly, the balancing of the internal tension of the design for children requires sophisticated solutions, because the needs of the actual users are often (mis-)represented by the desire of their parents. Therefore, in addition to satisfying social needs, the designers should also recognize the collective unconsciousness of adults who express on behalf of children. Taking the studies in Developmental Psychology and Anthropology as reference, this article focuses on playing, instead of knowledge acquisition, and discusses the balancing of the internal tension of the design of playing spaces for children, especially for the preschoolers. This article aims at revealing the role of games to children’s psychological and intelligence growth, as well as their game playing mechanism, by answering two questions: why do children play games and how do they play? By illustrating a case study on the playground design of the COBY Preschool in Japan, the proposed concept of “design to not design” is expected to inspire the design of children’s playing spaces.