This past spring a mom was doing a return up at guest services, with her two kiddos, who were probably about 3. I was GSA that night and happened to be walking by. One of the kiddos decided he was going to hit his sister. So he did. She started crying, and hit him back. So he started crying, and...yeah, vicious cycle. Poor Mom just wanted to do her return. So I walked up to them, knelt down at their level (they were strapped in the kid cart seats) and asked them if they had seen the movie Frozen. The girl, of course, answered she had, while the boy just sat there and stared at me trying to figure out why I was talking to them so calmly. So the girl and I talked about Frozen, and I had her tell me all about it. Mom was able to finish her return, and get back to refereeing the kids and the entire front end had peace and quiet.
I know how easy it is to want to grumble at kids when they are being obnoxious. And at a certain age, I'm likely to lose patience with their tantrums. But when they're little, sometimes a distraction of a calm voice is enough to quiet them down to either talk to you or at least stare at you in confusion. It will give the parent enough time to get done what they are trying to get done and get them out of there and everyone back to some semblance of quiet again. It doesn't always work, but when it does, you will be considered a miracle worker for the rest of the day.