I'm not kidding. This is a serious question.
Let me anticipate the obvious counterargument by acknowledging that anyone who wants to have a basic discussion of world events needs to know these facts, off the top of their head, because without them you can't reason logically about the news. But that brings us back to the original problem: Why would American kids want to have a discussion of world events? There is almost nothing in American journalism to inspire them. The published news in the U.S. is propagandistic, sensational, vapid, unenlightening, and often flat-out false -- and that's the New York Times and the Washington Post! The situation on CNN or (god help us) Fox is far, far worse.
Without any motivation to know the timeline of World War II, it becomes a piece of trivia: A random fact that is not especially useful. The ability to memorize trivia used to be considered a sign of intelligence; Google, Wikipedia and the iPhone are going to change that.