My three year old wears a mask every day at daycare. It's required. My five year old wears one for Kindergarten every day too, where it is also required.
Last year when my youngest was two, she had a hard time wearing one all the time, especially when we first starting going back to day care. But she took to it pretty quickly once she realized she didn't have a choice. Every time she took it off, a teacher made her put it back on again.
Basically, if you don't give kids an option to not wearing it, they figure it out like anyone else. You might not want to do that, but that doesn't mean you can't get kids to effectively wear masks. You can, and if it is required, the teachers at their schools will do it for you.
And it's not child abuse to make a kid do something that they don't really want to do. If it were, homework would be categorically illegal. I know you didn't assert that, but some actually have, like Tucker Carlson.
Schools ought to be able to mandate them if they feel the need. Some rural districts with low case counts might not feel that it is necessary, and that is okay. But you shouldn't take away a major tool that a school can use if they are actively fighting an outbreak.