That's so C....

Z: E, we need to talk. I have to tell you something.
E: Do you want to play my game?
Z: Yes. But I don't like it when you call me that. I want you to stop.
E: But you are......
Z (on the verge of tears): But I don't like it. (to me) Can you ask E to stop?
At this point I'm trying very hard not to laugh. I make a serious face to match the situation and say in my best "grown-up voice" - "E, stop calling Z that. Z, maybe E will stop saying that if you stop paying attention to her".
The word that was causing all the trouble? Cute of course!