The COVID-19 pandemic has accelerated digitization, access to IT resources, and digital inclusion in the Italian school system. This paper presents D-UDA (i.e., "unità didattica di apprendimento digitale", in Italian), a digital didactic unit for learning mathematics concepts. The presented approach combines teaching methodologies and game-based activities (e.g., the escape room) with a multisensory approach to designing and developing digital and multimodal technologies. D-UDA is divided into two parts: the first part consists of logic puzzles that adhere to the guidelines set by INVALSI (the Italian "Istituto Nazionale per la Valutazione del Sistema educativo di Istruzione e di formazione") for mathematics learning, while the second part involves a series of multisensory games designed to promote the development of transversal competencies, such as cooperation and engagement. Moreover, D-UDA encourages children to create their own adventure using the same tools employed by the designers to develop the experience. The children who participated in testing D-UDA in June 2020 were asked to complete usability questionnaires after the experience. Preliminary results indicate the effectiveness of the educational intervention presented, which integrates recent pedagogical theories and teaching methodologies with a multisensory perspective and a technological design.