This thesis presents a series of design-oriented studies for investigating and describing communication involving children with severe speech and physical impairments (SSPIs). The overarching goal is to inform how designers conceptualise communication that involves children with SSPIs beyond a widely cited view that communication centres around speech and happens at the level of the individual through the transmission of information. Instead, by positioning communication as co-constructed, situated and multimodal, the goal is to stimulate how one designs for digitally mediated communication by applying multiple, alternative frames that acknowledge these features. In order to achieve this goal, qualitative empirical fieldwork is undertaken that examines the everyday communication experiences of five children who have SSPIs. Drawing on theoretical influences from multimodal social semiotics and participatory design, study one and two investigate child centred accounts of communication involving children with SSPIs and their peers. The focus is on investigating communication, first in formal learning contexts involving existing augmentative and alternative communication (AAC) technologies, then in broader contexts beyond AAC use. Multi-layered perspectives are generated that consider: 1. a child’s view, by attending to children’s values and choices of modes; 2. an interactional view that attends to how communication is co-constructed in situ with other people and material objects, and; 3. a structural view, that examines the orderings of people, material objects and activities within an environment. These layered understandings produce research frames that are then utilised in study three. A design documentary is created and used to motivate design work for supporting face to face communication involving children with SSPIs and their peers with a team of designers who do not hold fixed orientations to designing assistive technologies. The findings of the three studies make three new contributions to the fields of HCI and AAC. First, the findings produce a theoretical perspective on communication, acknowledging multiple modes and displacing the taken for granted centrality of language. Second, the findings reveal design opportunities for new and existing technologies. Third, the studies contribute methodological insights for design work by considering ways of involving both children and designers when designing with and for children with SSPIs.