It depends. I think a lot of people do the "catch up" with their party thing. Where the whole family is waiting in line to meet Ariel, for example, then the littlest has to go pee and they don't want to lose their place in line so someone stays in line and the others go off to the bathroom. This really doesn't bother me. I know there are arguments about it but i don't have a problem with it. In the end i'm not losing any time by letting them back into their spot.
Then there's the groups that try and claim they have friends up ahead and are trying to catch up. You can usually tell the difference or at least have a feeling if they are full of "honey" or not. These types of incidents i have a hard time keeping my mouth shut. I had it happen on Splash mountain once and let the people cut but as soon as a saw a CM i told them and the CM DID in fact make them go to the end of the line.
Oh, I wouldn't care about a parent bringing the child to the other parent. I have a 5 year old, so I'm sure there will be lots of potty breaks. I mainly meant random people just getting in the line from no where.
I'm glad the CM made them move to the back!