The children with no organs

This story begins with a man and a woman who want kids but as luck has it nither could produce nor bare one. Going the extra mile instead of adopting a child they wanted one of there own blood.
they find a witch up in the mountains who has told the couple that she can give them the child but at a price. The child's organs will never be given to them. If the child were to have there organs they will know that there zombies and they will be a walking plague.