Preschoolers and masks in school

I understand the efficacy of masks in relation to covid.

But on preschoolers - to wear them all day? I don’t think that’s realistic. They’re going to be touching them all day which will probably spread the virus further. And I haven’t seen any studies about the negative effects of wearing masks all day. I understand the importance (decrease spread of covid) but it certainly can’t be good for your body to wear one all day.

And now my kids school is saying asthma doesn’t make her exempt for wearing a mask?

I don’t get it