This kind of thing was commonplace in the houses of old. Parents would have relations while the kids were around. In the case of Puritan households they all slept in one big bed while the mother and father went at it.
I don't think it is easy to hire a baby sitter in Japan.
It's really not; you'd usually use your relatives (or other parents with kids of similar ages) for babysitting needs, even if you had to travel to a different city (or prefecture!) altogether to do so.