It is work. How come it's work, or a job, if you're getting paid for it as a chilcdminder, say, but it' not a job or work when it's your own children?! And you do far longer hours, without days off, than a childminder does.
Also, being a SAHM is not the same as being a housewife, for those equating the two. Some women are housewives and they've never so much as held a friend's baby. Many women are SAHMs and they don't do all the housework, nor even the majority of it. SAHM means looking after your child or children. Yes, you have to do housework as it crops up, but that doesn't mean all responsibility for everything else in the home should be yours. Well, not unless you've had the bad luck to end up with a lazy, sexist twat.
If you're a SAHM, that is most definitely work. Studies have shown that if SAHMs were paid the equivalent of what others in paid employment would receive for doing the same activities for a wage, they would receive upwards of £80K pa - and that's only counting 9-5 hours.
Also v dismayed by the internalised sexism on this thread, with lots of mothers eager to dismiss, minimise or reject how much effort goes into mothering, or to not see it as worthy as paid employment.
Perhaps if caring, of all types, was more respected in our society, mothering would get the respect and maybe even renumeration that it deserves.