This is an open-label, Phase 3 clinical trial evaluating the efficacy of Tofacitinib based on remission in children with moderate to severe ulcerative colitis. The effects will be evaluated during an induction, maintenance, and extension period of taking the medication. Physical exams, blood and stool sample collection, and sporadic endoscopic evaluation are planned to take place throughout these periods.

Kids with IBD (inflammatory bowel disease) often struggle with tiredness and difficulty doing everyday activities, which can make life harder, but there aren't good tools to measure these problems in children. This study aims to create special tools to measure fatigue and disability in kids aged 2-18. Researchers will talk to kids and their parents to find out what issues matter most and use this information, along with medical records, to design the tools. The goal is to help doctors track these problems better and improve care for children with IBD. This study is being done in collaboration with the Shaare Zedek Medical Center. Participants will be compensated for their time and effort, upon completion of the interview.