Crohn's Disease: Efficacy, Safety, and Pharmacokinetics of Upadacitinib in Pediatric Subjects With Moderately to Severely Active Crohn's Disease

Inclusion Criteria: * Weight at Screening and Baseline must be \>= 10 kg * Moderate to severe Crohn's Disease (CD) defined as Pediatric Crohn's Disease Activity Index (PCDAI) \> 30 and endoscopic evidence of mucosal inflammation as documented by a centrally read SES-CD of \>= 6 (or SES-CD of \>=4 for isolated ileal disease) excluding the presence of narrowing component. * Documented diagnosis of CD prior to Baseline, confirmed by colonoscopy during the screening period, with exclusion of current infection, colonic dysplasia and/or malignancy. Appropriate documentation of biopsy results consistent with the diagnosis of CD, in the assessment of the investigator, must be available * Demonstrated an inadequate response, loss of response, or intolerance to corticosteroids, immunomodulators (IMMs), and/or biologic therapy or in whom use of those therapies is medically contraindicated. For participants in the US and South Korea, participants must have demonstrated an inadequate response, loss of response, or intolerance to one or more anti-TNFs (tumor necrosis factor). Exclusion Criteria: * History of: * A diagnosis of CD prior to 2 years of age. * Currently known complications of CD such as: * Active abscess (abdominal or perianal); * Symptomatic bowel strictures; * More than 2 missing segments of the following 5 intestinal segments: terminal ileum, right colon, transverse colon, sigmoid and left colon, and rectum; * Ostomy or ileoanal pouch; * Surgical bowel resection within the past 3 months prior to Baseline, or a history of more than 3 bowel resections. * Japan participants only: positive result of beta-D-glucan or two consecutive indeterminate results of beta-D-glucan during the Screening period (screening for Pneumocystis jiroveci infection) * History of any of the following: * Current diagnosis of ulcerative colitis (UC), indeterminate colitis, or monogenic inflammatory bowel disease (IBD); * Fulminant colitis or toxic megacolon; * Gastrointestinal (GI) perforation (other than due to appendicitis or mechanical injury), diverticulitis, or significantly increased risk for GI perforation per investigator judgment including history of volvulus and/or intussusception (telescoping of bowels); * Current diagnosis of any primary immune deficiency * Conditions that could interfere with drug absorption including but not limited to short bowel syndrome or gastric bypass surgery; subjects with a history of gastric banding/segmentation are not excluded.