"H, I want to get on the same page about how you handled the change in plans with D7 last week. I felt you put her on the spot, as she agonized about it on our way home. You also didn't ask me if I had plans. So in the future, if you have any inkling that you're going to want to do a switch, will you please talk with me privately first?"
Our S agreement spells out that schedule changes are to be handled between the two of us, kids are never to be put in the middle. If this had happened to me, I'd handle it pretty much exactly this way.
