In the Netherlands, approximately 1 million children (0-25 years) have a chronic disease. Above and beyond the ever-present challenges of growing up with an illness, these children have 40% chance to develop psychological problems, including depression, anxiety and loneliness. Throughout their life, this translates into decreased well-being and reduced social participation and generates additional costs for society. Early prevention of psychological problems is thus key to break this vicious cycle. Therefore, eHealth applications are promising. However, scientific knowledge is missing and validated tools are not yet available for this group and involved health care professionals. Our mission is to make scientifically validated eHealth tools that allow personalized and trans-diagnostic prevention of psychological problems widely available for this highly vulnerable group of chronically ill children and future adults, through an accessible, user-friendly, safe, and sustainable platform. To succeed in this mission, we present an iterative learning cycle approach in two four-year phases during which we gather the insights, and develop, evaluate, and implement the much needed eHealth tools: I. Development: Distil and validate the theoretical and game-design factors that make eHealth effective for chronically ill children. II. Evaluation: Evaluate trans-diagnostic and personalized eHealth tools for chronically ill children, using and developing state-of-the-art methods. III. Implementation: Study and remove the barriers that currently hinder implementation and uptake, and threaten availability of eHealth applications for chronically ill children. Our eHealth junior consortium includes (applied) researchers, pediatricians, psychiatrists, psychologists, patient organizations, knowledge centers, game designers, industrial designers, insurance companies, and business professionals. We will collaborate with the end-users (children, families, and professionals) in order to achieve both international scientific breakthroughs and optimal clinical and societal impact. Knowledge utilization is a crucial part of our project.