The purpose of this study is to evaluate the efficacy of ustekinumab dosing in inducing clinical remission (Global) and in maintaining clinical remission (US); to evaluate the safety profile and ustekinumab exposure (pharmacokinetics [PK]) in pediatric participants with moderately to severely active Crohn's disease.

Inclusion Criteria:

• Have Crohn's disease or fistulizing Crohn's disease with active colitis, ileitis, or ileocolitis, confirmed at any time in the past by endoscopy and histology
• Must have moderately to severely active Crohn's disease (as defined by a baseline Pediatric Crohn's Disease Activity Index [PCDAI] score greater than [>] 30); have ileocolonoscopy with evidence of active Crohn's disease defined as presence of ulceration (which is equal to Simple Endoscopic Score for Crohn's disease [SES-CD] score greater than or equals to [>=] 3) during screening into this study. The ileocolonoscopy procedure must occur within approximately 3 weeks prior to the administration of study intervention at Week 0 (Induction Period). A video ileocolonoscopy recorded within 3 months prior to the Week 0 (Induction Period) visit may be used in case of rescreening of a participant who had an ileocolonoscopy but failed the initial screening for another reason, on a case-by-case basis, after consultation with the sponsor. If unable to evaluate ulceration due to stricture or inadequate bowel preparation, at least one of the following criteria may instead be applied: an abnormal C-reactive protein (CRP) (> 0.3 milligram per deciliter [mg/dL] or 3.0 milligram per liter [mg/L] at screening) or; fecal calprotectin of >= 250 milligram per kilogram [mg/kg] or >= 250 microgram per gram [mcg/g] at screening
• If receiving enteral nutrition, must have been on a stable regimen for at least 2 weeks prior to induction week 0 (Week I-0)
• Females of childbearing potential must have a negative highly sensitive urine pregnancy test at screening and at Week I-0 prior to study intervention administration

Exclusion Criteria:

• Has complications of Crohn's disease such as symptomatic strictures or stenosis, short gut syndrome, or any other manifestation that might be anticipated to require surgery, that could preclude the use of the PCDAI to assess response to therapy or would possibly confound the ability to assess the effect of treatment with ustekinumab
• Have a history of latent or active granulomatous infection, histoplasmosis, or coccidioidomycosis, or have had a nontuberculous mycobacterial infection prior to screening
• Presence or history of any malignancy including presence or history of lymphoproliferative disease including lymphoma, or signs and symptoms suggestive of possible lymphoproliferative disease, such as lymphadenopathy of unusual size or location (example, nodes in the posterior triangle of the neck, infraclavicular, epitrochlear, or periaortic areas), and monoclonal gammopathy of undetermined significance, or clinically significant hepatomegaly or splenomegaly
• Have a history of moderate or severe progressive or uncontrolled liver or renal insufficiency; or significant cardiac, vascular, pulmonary, gastrointestinal, endocrine, neurologic, hematologic, psychiatric (including suicidality), or metabolic disturbances
• Received an investigational intervention including any investigational vaccines or used an invasive investigational medical device within 3 months before the planned first dose of study intervention or is currently enrolled in an investigational study; receipt of an investigational vaccine for Coronavirus Disease 2019 (COVID-19) is not an automatic exclusion criterion

The data sharing policy of the Janssen Pharmaceutical Companies of Johnson & Johnson is available at www.janssen.com/clinical-trials/transparency. As noted on this site, requests for access to the study data can be submitted through Yale Open Data Access (YODA) Project site at yoda.yale.edu

Induction period is an open-label period and maintenance period is a double-blind period.