I would say that's a cop-out.
Keeping order in the library is in her job description. I wouldn't expect the librarian to come up with some creative plan to keep my children in line. If my kids are misbehaving, she should be willing to say "knock it off!" or "get out of here!" That's all.
Now if my kids misbehave in the library on a consistent basis, it is my job to keep them from going there.
Kids need freedom to go places, and adults simply don't have the time or energy to monitor every single thing that kids do. Employees in public spaces have to be willing to step in when kids are out of line. They don't have to be substitute parents, but they have to let kids know in no uncertain terms when their behavior is not acceptable. A mall security guard should be willing to toss out kids who break the rules for example. And parents have to back up these employees.
Yes. It's supposedly "little" things like this that, when added up, indicate a collapsing culture. It's nothing to take lightly.