Sure. But what about federation? Arbitrary content is pulled from other instances. And my users are confronted with that content, too. Not only with each other. I'd need to also disable federation. (Or am I missing something?)
I think at that point I'd be better off installing Discourse or Flarum. And I've changed the whole vision of my instance. I've started with envisioning a federated platform that simultaneously can cater to adults and adolescents. And now I've locked it down to just cater to the few adolescents I directly invite, done away with the federation aspect and also cancelled all the appeal to adults. I think there's not much left of what I'd like.