Juvenile arthritis affects nearly 220,000 children and teens in the United States, according to the U.S. Centers for Disease Control and Prevention. This autoimmune disease causes joint pain, swelling, stiffness and fatigue, and can lead to long-term joint damage if left untreated. Although the exact cause is unknown, early diagnosis and treatment can help manage symptoms and improve quality of life. Treatment often includes medication, physical activity and regular care from pediatricians. Activities like swimming and biking are commonly recommended to help reduce pain and maintain mobility.