What should we do about our household workers (e.g. nanny, house cleaner, cook)?

One of the difficult things with COVID is that people are often contagious several days before showing symptoms, so asking the nanny to let you know immediately if they develop respiratory symptoms (and asking them to stay home if so) doesn’t perfectly protect you, but does help.  You could take it a step further and ask your household worker to stay home if any of their housemates or close contacts develop upper respiratory symptoms. And, certainly, if any of their close contacts had a known exposure to COVID, they should stay home.