There's a table at that first link. They started with 6 known cases of covid who interacted with hundreds of other kids at school, with zero transmission.
There's been plenty of evidence to suggest kids are less likely to get it, also less likely to pass it on, also less likely to be hospitalized or die and those who are tend to have other serious pre-existing conditions so they should absolutely isolate until vaccine. Kids in general just aren't as susceptible nor as at risk as say seniors are. Kids being at school also frees up parents to continue working, kids get their education, it gives some kids more access to food, saves families money not having to deal with daycare, and so on. As I said before though, I'm concerned for the adults who work at schools, and maybe high schools need more scrutiny than middle schools since a lot of the "kids" are almost adults too.