Your kid(s) are pre-teen so they'll soon be thinking and caring about things not related to people that are not related to them. It would be one thing if they were interested in the subject in which case I'd suggest maybe Amistad or that they read some children's books about it. There's one in particular I can't recall the title of but it was something Ike "they raised their hands to the stars" or something.

If this is something you're really concerned about (because your kids will be fine either way) then the best course of action (imho) is to have them get involved in activities where they can make friends who aren't white, all they need is one good friend of a different background to give them some perspective.