How Old are the Children?

Two college friends, Bill and Jim, meet on the street after not having seen each other in over twenty years. After learning that Jim is married, Bill asks him whether he has any children, and, if so, what are their ages? Jim recalls that Bill has always been quite the mathematician, and offers the following reply. "I have three children. The product of their ages is 36, and the sum of their ages is the same as the number on that house that you see directly across the street." Bill stares at the house reflectively, and then replies "Oh, come on. You'll have to tell me more than that!" "Alright", replies Jim. "My oldest child has red hair." Bill now correctly states the children's ages. What was Bill's response?