"if wearing mask were inherently dangerous, we would have hundreds of thousands of people in trouble because they were mask every day year after year after year."

 Nah they are all dumbed down now.


 I agree with the larger issue being the child development stages and how things like altered sleep, due to masks, and this can cause overlapping fatigue patterns, until they take the mask off for a day - like a weekend for instance.  I'm sure someone will Spin it to say fatigue means kids don't learn as well so they will all be dumb, but there is no evidence at this point, to show that fatigue permanently drops IQ.

 However I do recall when the oxygen inhibiting fitness masks came out they did find that children using one did actually gain more lung capacity.  The difference here is they didn't wear the masks all day.  So athletically they were slightly beneficial but they didn't use them enough to create a data-set regarding cognitive skills.  What they did notice is almost every kid pulled the mask away from their face instinctually to get more air, they didn't just maintain a level of discomfort for the funzies.

 I think the issue is if you want to think the education system to be less valuable today than it was X-years ago, or dumbed down, you will not require any evidence that masks made kids dumb.  If you don't really care, then you can recognize that its mathematically impossible to know right now because there hasn't been enough time to tell.

 My guess is these kids will still go to college, be able to drive, go get jobs etc.  They won't be recognizably inept and just plain dumb kids because they wore masks at school for a while.  I imagine most of them just pulled the mask away from their face, or wore it loose to be more comfortable anyway.  I could be wrong however, but my opinion is not fact so I won't sit here saying kids will for sure be dumb forever, or not dumb forever due to masks at school.