Looking for a story

I am trying to find this story that I have read before but I have forgotten the title.

The story is about a guy who has an highschool relationship with a girl but he moves away, years later when he has got a daughter with another woman he meets the highschool girl again and he finds out that he and her had a daughter. The woman and the girl end up moving in with the dad and the other daughter and the parents start to teach the children about sex.