This paper reports a design and implementation of a STEM enrichment programme infused with affective elements designed for Hong Kong students. Specifically, it features a design-thinking approach to develop solutions to a self-selected problem addressing the United Nations Sustainable Development Goals. Around 30 upper primary school (grades 5 to 6) and 20 lower secondary students (grades 7 to 10) enrolled in the study. Considering empathy as a core value of the design-thinking process and aligned with affective dimensions of thinking and learning, we investigate students' design-thinking development and STEM learning processes while highlighting empathy map as a pedagogical tool. We discuss the implications and insights of offering humanistic perspectives on STEM curricular design, especially for K-12 students. Our results showed that students at different age range were able to use empathy maps to devise designs effectively, despite their varying degrees of empathy. Furthermore, we conceptualize empathy maps as a pedagogical tool that creates physical boundaries in design thinking, making students' mental transitions across design stages more explicit. This study contributes to a better understanding of the educational potentials of design-thinking enhanced classrooms, with the results informing theoretical and practical advice on the integration of the empathy map in innovation-oriented projects.