It is unscientific (why should children and schools be magically exempt from transmission), flying against common sense, and there is evidence accumulating to suggest the opposite, albeit slowly and piece by piece, as schools have so far been open only in a very limited and speciifc way.
The biggest issue is they do know they're largely asymptomatic!
If asymptomatic people can spread it, or very low symptoms, we have no way of knowing where infections are coming from in childcare situations.
Classes of 10-15 then, low infections in community, few amenities open, sunny weather and many classes outside; the contexts are so different.
Now: classes of 30-34, higher community infection, more amenities open and demonstrating incidental clusters and outbreaks (around 100 from the football match in Durham) weather starting to turn. Failing testing.
It doesn't take a scientist to see the issues facing us. The fact kids are coming down with colds left right and centre isn't a coincidence!