One more point about this: I might feel more reassured about the lesser relative danger to children if there were any proven scientific explanations for it. Instead everything I've read involves a lot of hypotheses about T-cells and kids being exposed to other coronaviruses and such. Or, as
@acarey50 says, it may just be because we've done a better job of socially distancing our kids. The point is, we don't really know, and until we do we should proceed carefully and not jump to conclusions.
I was reading something recently about how, in previous epidemics such as the Philadelphia yellow-fever outbreak of 1793, there was a mistaken belief that African Americans were somehow less affected by the disease. As a result they were
recruited as caregivers for sick white patients, with disastrous results. Obviously, this is not the exact same thing, but one common thread that worries me is the potential for motivated reasoning. Benjamin Rush wanted to believe blacks were immune because he desperately needed nurses to care for patients; by the same token, we should make sure we're not convincing ourselves that children are safe just because we're so eager to have schools reopen.
To be fair, the opposite can also be true. We shouldn't seize on every data point indicating that children can get sick as "proof" that schools should remain closed forever. The difference, though, is that it makes more sense to err on the side of caution. I honestly don't know how much risk I would be putting on my kids to send them to in-person schooling, and while I'm open to whatever the data may ultimately show, in the meantime I'm not looking to play Russian Roulette with their health (or mine).