I can't fault Mrs. Fenn.
She told the management. I have learned myself, if I have a concern about other people's children, I either take it up with the children directly or bring it to the attention of a mutual authority. Going to the parents--never works, and all too often blows up in one's face. If the concern is serious enough that an outside party such as myself or Mrs. Fenn is involved, chances are the parents have already ignored the severity of the problem.
I've talked with other parents over the years and they have had the same experience. Going to the other parents? Never works and all too often makes things worse. You get either the downplayed response "She wasn't that upset, you're blowing this out of proportion" or "That's the best I can do, you tell me what you would have done, since you know it all."
At her age, Mrs. Fenn probably knew just as well, if parents leave their children alone in a room and return to find one of the children crying long and loud for them, in a complete melt-down, and then go out the next night doing exactly the same thing, then hearing from some old lady widow upstairs that they shouldn't do that--Oh, like that would change the McCanns' actions!