I don't have this issue anymore, but whenever it did happen I used the word rude. "Please don't copy what X said, that is rude" or I also use not nice in place of rude now because I have a new 1 year old and they need to learn how to play nice with the little one who can't talk yet but wants to do everything they do so it is "Please be nice and invite X to play".

I treat the kids like young adults and don't play games like doing the same thing back to them. I'll do that when they think it's funny, but not in a teaching moment.

You could also start out with simply addressing the situation on the spot and ask "Why do you keep asking what X asked?" or whatever the situation may have been so they get to think to answer.

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