My children (6, 4, 2.5) have been wearing them without issue, beyond that they occasionally slip off their faces if they're moving around quickly and we've tried a few different types. In our large metropolitan area, children are wearing them even walking in the park or out for a bike ride in the neighborhood when very socially distanced so I seriously hope people at a crowded spot like a theme park are willing to do the same.
We likely won't be doing Disney trips until things are more stable (and maybe not for a few years.. we're okay with that). But yes, I'll require them to wear them everywhere when we're back out in indoor public places. Our schools sound like they'll be asking children to wear them, come September, and I will 100% support that and send them off to preschool, PreK and 1st grade with them. Children with sensory disorders or other disabilities look like they'll be able to get a waiver exemption.