How old are your kids?

[AxyGaming]

Two men (Jim and Tim) have not seen each other in many years.


After talking for some time the following dialog occurs:

Jim: Are you married?
Tim: Yes

Jim: Have any kids?
Tim: Yes, three

Jim: How old are they?
Tim: You tell me!

Jim: I can't!
Tim: The product of their ages is 36

Jim: I still can't!
Tim: See the building across the street, count the windows
(Jim counts them)

Jim: There are....
Tim: Right, the sum of their ages is the same number as the number of windows!

Jim: I still can't
Tim: My youngest has red hair

Jim: I know their ages, they are...
Tim: Right you are!

How did Jim know???