Interesting question, I've thought about this myself. I don't have kids but am interested in hearing what parents have to say.

When I was growing up, I wasn't specifically made nigger aware, but instinctually I knew. I didn't grow up amongst them, and I could see they lived in the city and committed crimes, and I observed their behavior, etc.

Still, I think it would have been helpful to have some instruction. To me, the start is to give children a sense of identity, culture, of belonging to a group. If kids can self identity as being part of a human group, they can also see clearly, wait, look, there's a nigger and they are different from me. And at the crucial age they have to be told in no uncertain terms that mixing with niggers is not tolerated. To be sure, this risks a rebellion, but that is simply the risk that must be taken. Smart human kids of any age will understand this, they will not mix with niggers just to get back at you.