The notion of Calm Technology, which can move between our focal and peripheral attention, is a potentially valuable but underexplored concept in relation to smart connected toys. In this paper, we explored two interconnected research questions: (a) How can scaffolding support children in understanding Calm and designing for Calm connected toys? (b) To what extent can children contribute towards the design of novel connected toys that apply Calm Technology Principles? Building on UX practice and research we developed a participatory approach to working with children we call Design School, which gave children knowledge and experience of a design process. Additionally, we created design cards to use within the Design School, which scaffolded the inclusion of Calm technology design principles within children’s designs. The Design School workshops ran over four days in a U.K. school with 30 children aged 10–11 years, design outputs were analyzed to answer the research questions. From our experiences and analysis, we make four contributions: (a) the success of design cards as a tool to scaffold children in operationalizing unfamiliar design principles, (b) an understanding of how different design activities afforded expression of Calm in design ideas, and (c) the Design School workshop format, which proved effective in enabling children to engage in design activities.