When they say "Native American" don't they mean Indian? My son is seven and he was born in the United States, but on all those forms we have to fill out should I have been putting Native American all this time?
In Alaska the legal term is Native American. The legal world might have nothing to do with common language or everyday reality as we see it; although they use many words that are pronounced and spelled the same as ordinary words, the meanings are often very different.
I am what the PC call a "native American" but I always tell people that I am an American Indian, based on your point. Yet, I do believe and you do to, that your son is smart enough to know what is MEANT when someone says, "Native American".