If your child asks you why they keep using the n-word then explain it to them. Stop trying to change how history happened or how real life works.
It is bad enough that every period movie set these days glosses over what really happened in this nation's past, not to mention the straight up rewriting of textbooks that we use to "teach" schoolchildren about the past (African American brigades fighting for Stonewall Jackson - really, Virginia?).
Maybe they didn't think to include the n-word on any standardized tests, and that's why it isn't considered important.
Let's be clear on one thing. This revision is not taking place for some "politically correct" reason, or because some African-American or Native-American was offended. This revision is happening so white people can continue to believe the illusion that nothing wrong ever happened in America's past, ever, especially not at the hands of white people.
Do not be fooled.