I run a drama class, and without this method teaching would be impossible. They have to learn not to talk backstage, and it's a Herculean feat to get them to stop.
I tell them at the beginning of a rehearsal that if I hear anyone talking backstage the reharsal will be stopped and I will come back and find out why. If no good reason is given to me, everyone will be pulled out onto the stage and made to sit with their eyes shut in silence for five minutes.
I tell them that I know it is unfair on the quiet ones, but that the talkers give me no choice.
Any children who are worried about it either talk to me about it, or their parents do. Invariably the ones who worry are the ones who behave well, and I'm always able to reassure them and praise their behaviour.
I've found this method very successful when combined with a warning and praise for good behaviour. the children I teach are very happy. I know this, as if they weren't they'd leave! (I have a lot of competitors).
I rarely have to use this method with classes under 12 anyway.