You’ve probably heard of rheumatoid arthritis, an autoimmune disease and a chronic inflammatory disorder that causes the immune system to attack the joints. But what about when this happens in children under 17, not at the usual over 40?   This persistent joint pain, swelling, and stiffness in children is known as juvenile rheumatoid arthritis.  Interestingly, juvenile rheumatoid arthritis affects about 50,000 children in the United States alone.