China has said, (if they can be believed), that children 15 and under show a surprising immunological resilience to the virus, while also being one of the primary vectors for spreading the virus. (Or maybe because of their resilience, they are very good at spreading it? I don't know?)

In any case, that information seems to have been confirmed by the experience of Western authorities. So I'm inclined to believe it.

The idea here is probably to slow down the spread among kids now, which would slow down the spread to less vulnerable adult populations down the road. The drawback is that if some children are carrying the virus now, there is a short term danger to vulnerable adult populations.

I'm betting they've already wargamed all that out and the numbers right now favor accepting the short term danger?

They have not said they are primary vectors. That is not really known at this time.

It does if the virus has already been circulating widely. Which is why it's important to take steps like this early on. Provided other states or districts react differently, the estimation of efficacy will be very interesting to see after the fact.

Can you explain that? Just having the grandparents near the kids? I'd think that happens anyway... no one is suggesting people avoid their own family members, are they?

Yes. For not yet understood reasons, children do not seem to develop symptoms from covid19, but they can still be carriers. Combined with the fact that schools are essentially giant petri-dishes for disease, and old people are particuarly vulnerable to covid19, means that sending a child to grandma is essentially playing Russian roulette with her life.

I would go so far as to suggest that if she can take care of herself, grandma should self quarantine as much as possible for the duration of the crisis. People do not become less dangerous just because they are relatives.

After the family spent 2 weeks in self quarantine, visiting grandma is probably fine.

I have yet to see any solid evidence for this idea that children are significant sources of infection. Children tend to be less symptomatic, and while asymptomatic transmission almost certainly happens, every source I trust says it is rare and the main cause of infection is close proximity with someone who is showing symptoms.

At least in the US it is relatively uncommon to live with extended family like grandparents. If the children are already infected, then yes, a change in proximity to grandparents would increase the risk of transmission. If schools are closed before many children become carriers, then no, simply having grandparents near kids probably doesn't change much for the grandparents' risk.

The hope is that the kids aren't already infected, that seems like a very rare case. Sure it can happen, but they aren't yet recommending you don't even see family.

Many grandparents in the US live nearby and see their grandkids often and often look after them with some regularity. That seems to be the sort of scenario where they'd be employed to watch them while they are in learning from home situations, no? I don't think we are talking about frail people in nursing homes.

Yes, in fact they are.

Specifically, younger people are sometimes being told to avoid older people, sometimes when the older person is in need.

IIRC, some place had bans/restrictions on visiting nursing homes because the potential for spreading the virus might end up exposing a large percentage of the occupants to a significant chance of death.

No citation because I cannot remember where I read it.

Well I don't think the ones in nursing homes or "in need" are really likely to be recruited to watch the kids during the school days, will they?

You can be a grandparent of young kids very easily in your late 50s.