A lot of the American myth busting stuff on Cracked.com comes from this book
http://www.amazon.ca/Lies-My-Teacher.../dp/0743296281 and there's another great American myth busting book that I forget the name of right now.
What to teach children is not that easy a problem, there are shades of gray that are beyond a kid's ability to understand so you teach simple stories with heroes that not surprisingly are of the same culture/color as the kids being taught. Kids should feel good about the country they've been born into and their ancestors. You can't lay guilt and shame on 7 year olds, not healthy. I do think by high school it's time to stop teaching a sanitized version of history. But put history into its temporal context, that what seems evil or bad today would not be considered the same way in the 1500's.
The native Indian tribes of America were no innocents when it came to war, inter tribal wars were common and customs included 'scalping' and cannibalism. But their wars were not on the scale of war that European wars were fought on, simply because native Indians weren't very mobile, until Europeans brought them to America, there were no horses here.