A Study of How the Medicine Called "Etrasimod" Works in Children With the Gut Disease Called Ulcerative Colitis

The purpose of this study is to determine the safety, efficacy, and pharmacokinetics (PK) of etrasimod for the treatment of moderately to severely active ulcerative colitis in pediatrics participants (≥ 2 years up to \< 12 years of age). Participants who will complete the total 52-week treatment period will have the opportunity to continue in a Long-Term Extension (LTE) Period of up to 4 years (5 years after study enrollment).