Millions of people can't work on reopening other things without reopening those first.

THere'sno denying the importance of child care, but it seems just about guaranteed that if there is a case in one family it will spread to the other (up to) 11 families in the child's "stable group"

That's always going to be the risk until we have a working vaccine though and it's really hard to reopen without childcare in place. Without it a lot of people will have to choose between losing their jobs when their employer reopens or getting adhoc in home childcare.

If we're adapting anyway, one change could be gradually leaving kids home alone for longer times.

"Kids always need supervision" is a US thing. Leaving kids alone for some time works just fine in other countries. Of course there would have to be law/regulation/policy changes (to keep CPS away) but so what.

They were already open. It's expanded from "essential workers" to "businesses that are allowed to have facilities open". (not much of an increase?)

Some are already open, but with strict limitations. It won't be the same as re-opening as it was before; there are restrictions on capacity (12 max per teacher), sanitizing procedures, PPE for staff, guidelines around child health and reasons for exclusion, drop-off/pick-up procedures, and so forth. It's also not a carte-blanche reopening for all; the focus is still on essential workers.