The term juvenile arthritis (also sometimes called childhood arthritis or adolescent arthritis) is commonly used to refer to many conditions, such as juvenile rheumatoid arthritis and juvenile idiopathic arthritis. Arthritis in children and adolescents is relatively rare. Every year arthritis affects about one child in every thousand. Fortunately, most of cases are mild. But about one child in every 10,000 will get severe arthritis that may require treatment into adulthood.