Transition to adult care is an unavoidable and challenging period for patients and their families, and comes with adverse outcomes in experience of care, population health, and costs. Parents of children with chronic conditions report a greater need for support around the time of healthcare transition. Providers report neither having the tools nor appropriate resources to foster smooth transitions for patients and their families. We hypothesize that an app-based transition toolkit (named MyTransition) designed to support youth moving from child to adult care can improve their experiences and lead to better health. The main objective of this study is to collect information to design a large multi-centre randomized control trial to assess implementation of the MyTransition app including recruitment, completion of follow-up, and scale-ability of the intervention. The secondary objective is to assess the feasibility and potential effect of the MyTransition app-based transition toolkit for improving health of youth (quality of life), healthcare transition experience, and achievement of health and life goals.