A complication during a scheduled surgery means that a child patient is heavily bleeding and needs a blood transfusion. However the patient is a Jehovah's witness and the parents do not want the child to have a blood transfusion. What do you do?

Cannot do anything against the parents will as they have to give consent to anything that happens to the child. Obviously cannot wake up the child to check for competence as it is an emergency situation. So all you can really do is just advise the parents the implications of what will happen to their child if they do not allow the blood transfusion to happen. Mention that the child is at a severe risk of death.