I am saying that narrowing the discussion to "otherwise healthy children" is a reductive to a silly degree. The point is to protect all children, many of which are not otherwise healthy, or for that matter, may become unhealthy at some point.
You'd close schools to protect a minority of children with comorbidities from a virus which doesn't threaten the vast majority of children, knowing that school closures will definitely damage all children?
Is it really true about "vast majority"? In US, at least, it seems that the number of children with comorbidities such as obesity would actually be pretty high. You could argue that it's still a minority so long as it's under 50%, but I think that closing schools to protect, say, 20% of kids from a virus that can kill them is eminently reasonable.
