I hear your question, but the statistics show the chances of a kid chas vshalom dying from this is EXTREMELY low (almost non-existent). They’re much more likely to chas vshalom die in a car accident. Now, it says in the messilas yesharim “yeish yirah vyeish yirah,” there’s the good type of fear, which is for a danger that’s common to happen (ex- very likely to cvsh’ get run over if one isn’t looking both ways before he crosses the street), and the bad type of fear for an uncommon danger (ex- very unlikely to cvsh’ get murdered in a safe neighborhood). For the common dangers, Hashem gave us seichel to use. He WANTS us to put in the hishtadlus to defend ourselves from that (and is in fact a mitzvah). But for the uncommon dangers, we need to have bitachon, and if Hashem wants to cvsh’ have someone get hurt by a danger like that, they wouldn’t be able to prevent it anyways.
Now, you can say there’s no concern for the kids, but maybe they’ll infect older people. I certainly hear that argument, but be aware that:
1) There are some studies out there showing it’s POSSIBLE kids don’t infect adults (of course we don’t know for sure, so we should still be careful)
2) Many people already had the disease, and it seems VERY LIKELY that the anti bodies will make them immune at least for a short period of time (many health experts say that, and the fact that they haven’t been able to find any solid cases of reinfection despite this circulating the world make it seem very likely).
3) It could be the Yeshivas are still trying to be careful with some social distancing rules.
4) It could be many of them aren’t fully aware how contagious this is, or how many asymptomatic cases of this their are. Let’s be dan lkav zechus, please.