Wow, thought-provoking! My biracial boys are a little older than yours (18 and 20), and I have never had to think this through. It's just never happened in our household (my wife is Black and I'm white). It isn't like we banned it, aforethought. We live in NYC, so it's certain that my kids have been around other kids who indulge in casual usage of this word. But I can't imagine my wife allowing the word in our household, regardless of whether its usage included one final phoneme versus another...