I have to say something here. You do not know the situation here, other than the kid got out of line, and they had to start over. Maybe, this was 14th time that day she got out of a line that had a long wait, maybe the family was getting tired of waiting in a line, getting halfway there, or whatever, the kid pops out of line, they chase after her, they have to start at the end of the line again.
My DD has a FASINATION with public restrooms. I have no idea what it is about them, but we cannot walk past a public restroom without her announcing she needs to go. I KNOW she does not need to go. It took me a long time to figure her out. We would be in WDW, heading to some ride, and she needs to go, we stop, take her to the bathroom, for what? I wait, and wait, I hear NOTHING coming from her stall. Meanwhile, we could of been there by now. I ask what is taking so long, she then announces, she doesn't have to go. After awhile, it gets BEYOND frustrating. BTW, this happens other places besides WDW.
Last trip to WDW, we were heading to Mexico for the boat ride, of course we pass the bathrooms. DD stops everyone in their tracks, to announce she needs to go. even though we just had a potty stop after we entered Epcot. I told her no, we were going, she could wait. She starts to hold between her legs and dance around, she really needs to go she whines. I still say no and keep walking. she starts to cry, and I am beyond frustrated, but I give her the benefit of a doubt, AGAIN, and take her to the bathroom. We go in, and sure enough...NOTHING. This after I was stern with her about how I knew she just wanted to go into the bathroom, and she insisted she had to go. I demanded she come out, and I was letting her have it. (yelling at her) There were some women there, but I was not paying attention to them. As she was washing her hands I was telling her that she was not going to announce any potty breaks for the rest of the day, so when anyone had to go, she better make sure she went then, because she was not going to have another chance. I am sure those women thought I was being terrible to her. I had had it!
Later that day, I did have to go tot he bathroom, and so did she ( she is not a camel after all

)We were at the sinks washing our hands, and two women were there, and I heard one say 'oh , there is that poor little girl that was being yelled at this morning"
I wanted to tell them to MIND THEIR BUSINESS. They had no idea what I had been through with my DD, and having to drop everything to take her to the bathroom.
In another life, I might enjoy spending my days going from one public toilet to another, but right now,it is not my idea of fun.
So, please do not judge someone because they are upset at their kid. You don't know what might have happened in all the earlier hours of the day, for her parents to reach that point.