>I'd argue that US parents are so keen on schools staying open because often their jobs depend on it. I expect it would be similar in Japan as well.

Why would it be similar in Japan? In Japan, children walk themselves to school (using public transit if necessary) as young as 6 years old. It's not like the US where parents can be thrown in jail for "child neglect" if their children don't have 24/7 adult supervision. I imagine that Japanese schoolkids can just stay at home if the schools are closed.