"Scenes from a Group Marriage" short essay at Salong.com

http://www.salon.com/mwt/feature/2008/06/04/open_marriage/index.html

reviews one man's experience as a child in the 1970's when his parents and another couple decide to get together. FYI.

ETA: Whoops, that should be Salon.com. My fingers are really fumbling that today.

I find it odd that it sounds like the arrangement was never discussed with the children -- not even to inform them about what was going to happen.

Well, it was the 70s. It was very uncommon to tell children anything about their parents' relationships. I remember one Christmas when my father's secretary came for the holiday and then we never saw her again. I know in retrospect that my father was sleeping with her. My mother found out and insisted that, if my father was thinking of getting a divorce, that the other woman at least meet the children. But we certainly had no idea what was going on. (I sometimes wonder if the secretary decided she didn't want to put up with two surly teenagers less than 10 years younger than herself and that's why the relationship ended.)