This paper is based on outcomes from SID (http://sid.desiign.org), a three-year project where twenty-four children with profound intellectual disabilities visited three MSE centres. SID's aim was to develop and demonstrate the potentials of interactive design in and for MSE practices together with the children and the pedagogical staff. In the project, we developed artefacts that were designed to be part of and mediate the explorations rather than to become end products. The designs were explored by the children at the MSE centres and further developed depending on what the children did and what seemed relevant to them. There are few documented examples in the literature where children with profound developmental disabilities are involved as active participants in design activities. We present and discuss the participants' roles in SID's research and development process based on experiences and material from the project, with a hope that this paper can serve as an example of what such a development process might look like and as inspiration for future initiatives.