Operation of our economy relies a lot on free or paid labor from old people, though. We can't isolate them and keep the economy running normally.
How do you think poor people get child care so they can go to work, for one thing?
I do think there's room to criticize what was done, but I don't think "just isolate old people" was ever a practical option, and I don't think the alternative of "we're keeping things open and not isolating old people, so make sure you say anything you've been meaning to to your elderly parents really soon, because... well, you know" was ever gonna go over well.
> I think it's fair to question whether it was "reasonable precaution" to shut down schools,
I know enough teachers and was privy to their thoughts and observations during the pandemic that I'm quite confident schools were going to shut down no matter what official policy was. Lots of teachers are married to higher earners, and they're basically all working because they want to. They'd have stopped wanting to, and the schools wouldn't have been able to remain open with normal hours and procedures, with their much-reduced staff. A couple districts I know for a fact faced near-revolt over measures that were regarded as insufficient and coupled with tone-deaf messaging, and had to adjust or the scenario above was definitely going to happen and they'd have lost 10+% of their staff all at once, which is enough to completely mess them up.
Whether their opinions were based on reality hardly matters: fact is, schools were going to shutdown, one way or another.