Additional Study Information: This study is evaluating an investigational medication to see if it is safe and if it works well in children andadolescents who have mild to moderate ulcerative colitis (UC) or are in remission. Ulcerative colitis (UC) is a chronic disease of the last section of the intestine, which is also known as the colon. If you have UC, the lining of your colon becomes inflamed and forms ulcers. UC often causes pain, bleeding, and loose bowel movements. UC is different from Crohns disease because UC only affects the lining of the colon. Crohns disease can affect any part of the gastrointestinal tract. UC is also different from irritable bowel syndrome (IBS). IBS does not cause inflammation of the intestinal tract. The goal of the study is to learn whether an investigational medication is safe and if it works well in children and adolescents aged 5 to 17 who have mild to moderate ulcerative colitis (UC) or are in remission. The investigational medication is already approved in multiple countries to treat UC in adults. Because it has not been approved for children and adolescents, it is considered investigational in this study.