Design of new technology with children has been widely investigated, and lately several workshops have been organised with children for designing novel IoT or smart objects, e.g., for smart cities or parks. Gradually, the research focus has shifted, from an analysis of the technology itself, which children help create, towards an analysis of children's possible gains in design workshops. However, in spite of several recent efforts, it is still unclear what happens when children participate in diverse parts of a design process, ranging from ideation to prototyping. This paper investigates it, focussing on children's gains in relation to their knowledge of design. A structured design workshop can help obtain such gains and analyse their achievements. Therefore this paper presents a structured design workshop with 27 children, aged from 11 to 14 years old, ideating, programming and prototyping smart objects for their town park. The workshops was structured and centred around a board-game with cards, so as to playfully make children reflect about design, and promote their awareness of what they were doing. Data were gathered in relation to children's reflections from different perspectives, during the workshop, and in relation to their awareness of design, after the workshop. The analysis of the gathered data suggests that the workshop positively affected children's reflections on design and awareness of design, giving indications for future work concerning critical design with children.The order of authors is alphabetical. All authors gave major contributions to the research. In particular, Gennari supervised the overall research design, and acted as moderator. Matera supervised the data processing, and acted as moderator. Melonio supervised the game design, and acted as moderator. Roumelioti developed the game design, and acted as technical facilitator. Rizvi managed the electronics and developed programming snippets for the programming and prototyping part, and acted as technical facilitator. All authors contributed to the paper writing, which was coordinated by Rosella Gennari.