fwiw, when it looked like my wife and I were going to D (or at least S), we did kind of do it in "phases" with the boys, first telling them that "Mom and Dad are having some problems," and then letting them know when we went to a Retrouvaille weekend, and then to an MC, and then we started talking to them about the two residences, etc.
I am NO expert on this subject, but I remember saying to the fetching Mrs. Puppy "I dunno, I feel like either we're way lowballing the kids on this, or else we've totally hit on a great way to handle it, because they SURE are taking it well."
My older son (now 16), particularly, does NOT like surprises, and doesn't handle conflict very well. Telling him in "doses", I think, made it easier on him.
I do feel, that HOWEVER you do it though, they need to be told SOMETHING like YESTERDAY, because -- as you've noted -- their friends' parents know, and it's only a matter of time before they hear something from someone OTHER than their parents, which would be horrible.
