Which is correct?: men, women, and children. Or men, women and children.
Some authorities, including many newspaper style sheets, say that you don’t need a comma after the last item in a series when it is preceded by a conjuction. The reasoning is that the conjunction (e.g., and) separates the last item from the rest of the list.
Other authorities insist that you do need the comma before the conjunction. This so-called “Oxford comma” is necessary because a conjunction joins words. It makes no sense to have a conjunction both join and separate the items in a list. (This is the rule that I have taught and live by.)