I know that children seem to have been much less affected,
Some reports are suggesting that although younger children don't seem to be affected to the same extent it is likely they can carry it and spread it.
So you put classes of 45 together with one teacher and maybe a TA - well those school staff are going to be at increasing risk. Many teaching staff are also in the venerable groups remember as well - older, low immune, etc.
What school parents could be doing as well at the moment is trying to form small support groups where, incase of a school closure but not self isolation, they could get together and share the childcare. They may still need to miss some work, but if the share it out enough they could make it so that everyone only needs to miss one day a week, or even less. Then if they want the children to be contained and still learning, they can follow the planning, suggestions and worksheets which school staff could be sending home via online sites or email.
Like some others I am also sceptical that once the class restrictions are removed temporarily there will be some people high-up considering "well it worked for that time period' " so lets get rid altogether.