American Heritage Dictionary; Work, definition:

Physical or mental effort or activity directed toward the production or accomplishment of something. ”Cleaning the basement was a lot of work."

Such effort or activity by which one makes a living; employment. ”looking for work."

Again, kids are work. And since, as another lemming pointed out, some people do it as an actual job, it counts under both definitions.

And if you do hie off to the Bahamas, you still have to bring that work along. You can’t just leave it behind and just have a relaxing vacation with nothing to do. (Unless you find a babysitter, but then you’re not doing the work of childcare anymore; now you’re using maternal leave for something that isn’t work).