"I know through meeting MC that W has other ideas."
Take the reins and confront her on this. Tell her that you will not tell the children something that is not true. And that while you will not tell her what to say, that you do not agree to tell them that it is a "mutual" thing.
M-43 W-40 2D - 9 and 5
Emotion, yet peace. Ignorance, yet knowledge. Passion, yet serenity. Chaos, yet harmony. Death, yet a new life.