Everybody knows that Wikipedia, being crowdsourced and open to edits from just anyone and not verified by Trusted And Credentialed Experts operating under Layers Of Editorial Oversight, is utterly untrustworthy (don’t cite it in an essay, kids!). On the other hand, actual published paid-for books, printed on real paper and everything, are unimpeachable carriers of Truth and Knowledge (see Layers Of Editorial Oversight, above).
Eugene Volokh presents an example of well-known and disconcertingly uncontroversial Wikipedia articles which disagree with the printed historical record, or at least a part of it. It’s short, so I’ll quote it in full:
From the first sentence about World War II in All About World History (1999), a history book for children:
In 1939, Hitler (see below) sent armies to invade Czechoslovakia and Poland; Britain, France, and Russia decided to help the Czech and Polish people defend their lands.
Remember, parents: You don’t have to stop your children from looking things up on Wikipedia, but be sure they verify anything they find against a printed source.