Malignant disease and anticancer therapy dramatically affect daily life activities and participation in grassroots and high-performance sports. Specifically in childhood and adolescence such activities are relevant factors of individual development and social life. This review focuses on the inherent reduction of normal physical activity in pediatric oncology because this cutback additionally contributes to the level of burden of malignancies. Maintaining normality requires detailed analyses of disease-related and therapy-related restrictions and their justification. Relevant efforts should be stepped up to maintain physical activity levels during pediatric cancer therapy. Another aspect addresses direct therapeutic implications. Feasibility studies, nonrandomized as well as randomized investigations addressed therapeutic effects in acute hospital care, in bone marrow transplant settings, and in outpatient therapy. The overall summary shows positive effects on clinical and psychosocial outcome. Even if the basis of the data for children is still limited, there will be no doubt about a general impact of physical activity on acute side effects as well as late effects. In the areas of tension between context-related restrictions, the right to maintain normality wherever possible and the positive therapeutic and psychosocial perspectives of sports, strong efforts are needed to support physical activity wherever indicated, clarify contraindications, and overcome structural limitations.