Guselkumab will be administered intravenously.

Percentage of participants with clinical remission at Week 12 will be assessed. Clinical remission is defined as PCDAI score <=10.

Percentage of participants with endoscopic remission at Week 52 will be assessed. Endoscopic remission is defined as SES-CD total score <=4 and at least a 2-point reduction from baseline and no subscore >1.

Percentage of participants with corticosteroid-free remission at Week 52 will be assessed. Corticosteroid-free remission is defined as PCDAI score <=10 at Week 52 and not receiving corticosteroids for at least 90 days before Week 52.

Percentage of participants with sustained clinical remission at Weeks 12, 24, and 52 will be assessed. Sustained clinical remission is defined as PCDAI <=10 at Weeks 12, 24, and 52.

Percentage of participants with clinical remission by PRO-2 will be assessed. Clinical remission by PRO-2 is defined as stool frequency (SF) <=3 and abdominal pain (AP) <=1 and no worsening of SF and AP from baseline.

Serum concentrations of guselkumab will be assessed. Serum samples will be analyzed to determine concentrations of guselkumab using a validated, specific, and sensitive immunoassay method.

Ctrough is defined as the serum concentration of guselkumab immediately prior (pre-dose) to the next drug administration.

Change from baseline in body weight at Weeks 12, 24, and 52 will be assessed.

Change from baseline in body weight percentiles at Weeks 12, 24, and 52 will be assessed.

Change from baseline in body weight z-scores at Weeks 12, 24, and 52 will be assessed.

Change from baseline in height at Weeks 12, 24, and 52 will be assessed.

Change from baseline in height percentiles at Weeks 12, 24, and 52 will be assessed.

Change from baseline in height z-scores at Weeks 12, 24, and 52 will be assessed.

Change from baseline in height velocity at Weeks 12, 24, and 52 will be assessed.

Percentage of participants with clinical remission who were assigned to guselkumab dose regimen 1 and did not receive rescue therapy at Week 52 will be assessed. Clinical remission is defined as PCDAI score <=10.

Percentage of participants who achieve endoscopic response who were assigned to q4w maintenance therapy and did not receive rescue therapy at Week 52 will be assessed. Endoscopic response is defined as >=50% reduction (global) and >50% reduction (U.S specific) from SES-CD score at baseline.

An AE is any untoward medical occurrence in a clinical study participant administered a pharmaceutical (investigational or non-investigational) product that does not necessarily have a causal relationship with the intervention. An SAE is is any untoward medical occurrence that at any dose: results in death, is life-threatening, requires inpatient hospitalization or prolongation of existing hospitalization, results in persistent or significant disability/incapacity, is a congenital anomaly/birth defect, is a suspected transmission of any infectious agent via a medicinal product and is medically important.