One other thing not taken into account is that schools can have a low risk of infection. Now that children are home in confined structures with their parents, they can then be vulnerable if their parents are infected or at risk of it. This as opposed to the children going to school and being among people not infected.
Fortunately, the above scenario is likely to not play out as described. One Nobel Prize wining biological physicist at Stanford University states not only that the spread of the COVID-19 virus is slowing down, but that we are also naturaly immune.