My 5 year old comes up to me the other day and says, "Baba, why do some people say 'black people' and 'white people'".
Not knowing where he was going with that, I asked, "What do you mean?"
"Because", he goes, "everyone's brown. Some people are just lighter brown than others".

Now that I think about it, he's right. There is just one race, the brown people :).