This is an outpatient, 48-week open-label single-arm Phase II clinical trial of preemptive long-acting recombinant factor VIII Fc fusion protein, Eloctate, in children with severe hemophilia A to prevent inhibitor formation. Eloctate was recently approved by the FDA for the treatment and prevention of bleeds in hemophilia. In this trial, Eloctate will be evaluated in the prevention of inhibitors in children with hemophilia A. The research in this trial is considered greater than minimal risk as it involves initiating weekly dosing before the first bleed and obtaining special inhibitor studies. Preemptive refers to initiating prophylaxis before the first bleed. Prophylaxis refers to giving preventive factor to prevent bleeds. In this study, beginning at the age of 4 months, children with severe hemophilia A will be enrolled before the "first bleed," which for the purpose of this study will be the first bleed requiring factor treatment (excluding circumcision). A total of 65 subjects will be enrolled at one of up to 41+ HTCs, about 1-4 per site, including up to 4 at this site. Following enrollment, subjects will begin preemptive prophylaxis with Eloctate 50 IU/kg weekly before the first bleed.