You ask why white people teach this crap to children. The intellectual James Burnham correctly identified 40 years ago that the ideology of liberalism only makes sense when you realize that it is an ideology of civilizational suicide.
Obviously, there was little "diversity" or "multiculturalism" in the textbooks we used. What did we do? My parents, being proud of our racial heritage and wanting us exposed to it, made sure to support supplemental studies in black/African culture and history, which was reflected in our home and in many of the forms of entertainment we chose. I never owned a white doll.
At the same time, they made sure we were exposed to classical music, art, and other aspects of Western Civilization since that was the civilization we lived under. We read most, if not all, of the "Great Books." We were taught to appreciate other cultures, to the point that we sometimes went to school wearing green, carrying green cupcakes on St. Patrick's Day that my mother baked.
My point- instead of forcing the schools to teach "multiculturalism," particularly at the expense of the greatness of the civilization that has allowed us all the standard of living that we enjoy, parents and communities need to make sure their kids get exposed to the variety of multiculturalism that they want them to learn.