Do children with juvenile rheumatoid arthritis have to limit activities?

Only within reason: Patients with jra should avoid high impact activities such as running and are better to pursue non-impact sports such as swimming, bike riding, cross country skiing, etc. There have been however remarkable advances in treatment by dmards (disease-modifying antirheumatic drugs)that modify the body's response to infection and disease and may thereby allow unrestricted sport.

Yes: Ra (also called jia) for juvenille idiopathic arthritis is a disease of unknown etiology. There are many theories for why it happens, many believe there is a virus responsible. Pain and stiffness may limit activity. Appropriate treatment can vastly benefit the patient, and a pediatric rheumatologist can be your best friend.