I've taught the difference between a "high" or "whining" voice and a "low" or "pleasant" tone of voice. I tell them to try again in a pleasant tone of voice. We've practiced them at neutral times (they think the "high/whining" voice is hilarious when we practice
) so I can pull in that skill during a situation.
I also do "asked and answered" and, if really frustrated, I walk away. Mostly scripting them to try again in a low tone of voice works. At first I had to say exactly what I wanted to hear, then just "try again with a low tone of voice," now I just say, "Try again."