Roche is hoping to win a slice of the $11 billion-a-year hemophilia drug market with the drug, also known as ACE910 and designed to compete with more traditional treatments from Novo Nordisk and Shire.
Roche's drug is being closely watched because it could change the way the disease is treated.
Hemophilia patients, whose blood does not clot properly, need life-saving infusions of clotting factors, but development of inhibitors in many of those being treated can interfere with efforts to control their bleeding.
"At this interim analysis after a median of 12 weeks of treatment, emicizumab prophylaxis showed a clinically meaningful reduction in the number of bleeds over time," Roche said in a statement.
Roche said managing hemophilia A with inhibitors to factor VIII was especially challenging for children and their caregivers because bleeding was difficult to control and current treatments required frequent intravenous infusions.
Roche published encouraging data on the drug in December from a phase III study with adults.