When the kids (or even adults) complain, it is a form of criticism. If you did what I want, something else or something better, I wouldn’t be complaining. It is also a form of ingratitude. I don’t like what you’re doing; I want something else.
Philippians 2:14 tells us to do all things without complaining because it produces nothing that’s good.
I have also learned that my classroom is more successful when I teach my young scholars that if they want to bring up a complaint, they need to offer a solution to the issue as well. This is far more productive and less tiring.