This is a multi-center, open-label study to determine the safety and effectiveness (how well it works) of two standardized treatments called "mesalamine" (Pentasa®) and "prednisone" in children with newly diagnosed UC. Standardized treatments are types of treatments agreed upon and used by many qualified doctors. The medications being used in this study are considered "standard of care". Currently the ways in which these medicines are used (doses, frequency of dosing) may vary from site to site. This study will determine response to a standardized way of giving these medicines.