Design of assistive devices (ADs) requires clinical inputs from rehabilitation professionals alongside first-hand context and participation of patients who have special needs. Co-design or collaborative design is considered the best-suited approach for designing such systems where user groups are little or not well understood. However, it is rarely adopted for designing customisable ADs, though several studies have employed co-design approaches for other product solutions in various capacities for special needs. In addition, literature wields various terms like participatory design, co-creation, co-operative design, and collaborative design, sometimes used interchangeably, while others contend distinct definitions. Thus, a review of existing literature has been conducted to interpret various concepts of co-design for special needs through a theoretical lens. Further, an attempt has been made to assess the attributes of the variants of co-design undertaken and to comprehend the practical challenges in adopting the same for ADs, so as to provide an essence of the rationale behind co-design being apt for designing for special needs. This paper investigates co-design as the vehicle to engage multiple stakeholders and users, with diverse needs, abilities characteristics, and expertise and further prescribes a process support, ‘mCoDe’, for designers to undertake ‘multi-user-centric co-design’ of assistive devices for special needs groups like children who require a ‘voice’ on their behalf.