Thanks @noblegiraffe: it really helped!
So here's a long post but I found this stuff really helpful:
www.hsph.harvard.edu/news/features/coronavirus-covid-19-press-conference-with-bill-hanage-07-15-20/
Harvard T.H. Chan School of Public Health with Bill Hanage, associate professor of epidemiology and a faculty member in the Center for Communicable Disease Dynamics, speaking at a virtual press conference on July 15th. He:
• agreed that risk of death in children seems very low, however:
"as I’m sure you’re aware, when we start looking at these infections over time, we can see the proportion of them that are very long term or leave people with chronic illness. And potentially, have consequences that we’re only beginning to learn about because this is truly a multi-system disease. We think of it as a respiratory virus, but it infects way, way, way more than simply the respiratory system. And we can expect to see some of those consequences in the health of children going forward"
• says we don't have sufficient evidence about schools, and that older children may well spread more:
"But right now, what I’d say is that almost all the studies that we have about the role of children in transmission suffer from biases of one kind or another. However, it is plausible to think taking a read of all of them together, that younger children are somewhat less likely to become infected and maybe a little less likely to transmit. Older children behave much more like adults, and find social distancing is much more difficult. So that’s slightly older high schoolers and so. So, they should be treated separately"
• testing requires clear actions dependent on results (which apparently US schools haven't been given?!)
"So, think of it like this. Imagine you have one case. As I’ve said, this is not even just about kids. The finding of a single case does not necessarily mean that transmission has occurred. So if there’s one case and it’s a single introduction to the school, it’s unlikely, all taken together, to transmit. So under those circumstances, with a low rate of community transmission, it would probably be sensible to shift that group to education at home for a period of time, not necessarily very long, but for a period of time in order to check whether or not transmission had occurred. And that’s very different from a situation in which you are having an introduction into every school, into every class, you know, multiple times. Now, that means one of them is almost certainly going to transmit. The increase in the number of infected people, or potentially infected people, will be much larger. And at that point, the question becomes open as to whether or not the schools should be open at all.......
I think that if you can keep community transmission low, it’s reasonable to think that schools can reopen. And I think it’s reasonable to think that outbreaks within schools can be fairly readily controlled. Once community transmission gets high and the number of introductions to schools becomes high as well, then you’re in a different situation and you have to start thinking about doing something quite different."
and it depends if schools are more affected by transmission coming in from the community or vice versa:
"So, in other words, are the schools a net contributor to the transmission? And I think that at the moment, we don’t have enough data to say whether or not that no under (July: he means, there are no) circumstances under which that would be the case. But we do expect it to be the case, the higher community transmission becomes."
(Emboldening is mine - the especially quotable bits!)