Over the past 50 years it has become clear that physical inactivity is associated with chronic disease risk. For several rheumatic diseases, bed rest was traditionally advocated as the best treatment, but several levels of evidence support the imminent paradigm shift from the prescription of bed rest to physical activity in individuals with paediatric rheumatic diseases, in particular juvenile systemic lupus erythematosus, juvenile idiopathic arthritis, juvenile fibromyalgia, and juvenile dermatomyositis. Increasing levels of physical activity can alleviate several symptoms experienced by patients with paediatric rheumatic diseases, such as low aerobic fitness, pain, fatigue, muscle weakness and poor health-related quality of life. Moreover, the propensity of patients with paediatric rheumatic diseases to be hypoactive — often due to social self-isolation, overprotection, and fear and/or ignorance on the part of parents, teachers and health practitioners — can be detrimental to general disease symptoms and function. In support of this rationale, a growing number of studies have demonstrated that the systemic benefits of exercise training clearly outweigh the risks in these diseases. In this sense, health professionals are advised to assess, track and fight against physical inactivity and sedentary behaviour on a routine basis, as they are invaluable health risk parameters in rheumatology.