When it comes to exercise and sport for children and adolescents with cancer, there is often still the opinion that physical activity has a negative effect on the weakened body suffering from cancer. Many studies show that the opposite is the case: physical activity for children and adolescents with cancer do not jeopardise the success of treatment, but rather promote it. It has been shown that physical activity has a positive effect on motor skills, physical fitness, sleep quality, fatigue symptoms, body image and general quality of life in children and adolescents with cancer. In addition, physical activity leads to an improved fat-to-muscle ratio, metabolic status, bone strength and reduces cardiovascular disease. Furthermore, various studies show that oncological patients with sarcopenia (loss of muscle mass) and frailty have a poorer response to their cancer therapy. This broad spectrum of effects of physical activity leads to improved and faster rehabilitation, is directly linked to the success of treatment and has led to exercise being an integral part of treatment in many paediatric oncology centres worldwide. Furthermore, more exercise that includes playful cognitive tasks is expected to lead to improved attention, memory and academic achievement. Besides, it is important to try to get children to exercise at home outside of the inpatient setting. Hybrid (on-site and digital meetings) programmes also work for children and adolescents. Additionally, the research project offers sports counselling after the end of therapy to reintegrate the patients into everyday sporting life, be it in a club or at school. The central question of the research project is: Does cognitive challenging physical activity developed for children and adolescents undergoing acute cancer therapy improve cognitive and motor performance compared to a control group receiving standard care?