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).

Inclusion criteria: Have a diagnosis of ulcerative colitis (UC) that is moderately to severely active Participants are permitted to be receiving a therapeutic dose of select UC therapies Exclusion criteria: Severe extensive colitis Diagnosis of Crohn's disease (CD) or indeterminate colitis or the presence or history of a fistula consistent with CD Diagnosis of microscopic colitis, ischemic colitis, or infectious colitis