This trial is conducted globally. The aim of the trial is to investigate safety, efficacy and pharmacokinetics (the exposure of the trial drug in the body) of NNC 0129-0000-1003 (N8-GP) in children with severe haemophilia A who have undergone treatment with previous factor VIII (FVIII) products.
Inclusion Criteria: * Male patients with severe congenital haemophilia A (FVIII activity level below 1%) * Weight above or equal to 10 kg - Documented history of 150 exposure days (ED) to FVIII products for patients aged 6-11 years and above 50 ED to FVIII products for patients aged 0-5 years Exclusion Criteria: \- Any history of FVIII inhibitors