to me it makes total sense for a white (or black) kid, who's grown from a baby only seing people of his own skin colour, to be scared or at least wary of the big scary person who looks totally different to everyone he knows and trusts, that's not racism, I'd say it's closer to survival instinct, you know what 'good people' look like, from experience, and then something new and different comes along, and you're not going to like it.
However, that's where nurture comes in, that kid needs to be taught that people who look different are different in small ways but still just people, and are mostly the same as the rest of us.
This is the bit I think that bugs most people about the people who cry 'racism' at every opportunity, we're NOT all the same, we should be aiming for 'equal but different'.
I still think it's a shame we can't say stuff like 'black people are better at sport' despite looking at the results of the Olympics and the like, because some people decide there's some 'unwritten meaning' in that phrase. I'm not saying 'ooh they're good at sport, let's stop them being anything else, lets just train em to run around and win medals for us'.
I think he's been told some stuff about 'those scary black people' tho, and why he should hate them, and just needs to be told that he was told some very silly things and doesn't need to worry.
I do think there's a little bit in all of us tho. I don't know if this counts, but I know I feel kind of irritated when I'm sat on a regular bus, and end up between about 6 indian women who talk away in their own language thru me. I also know they've got every right to talk in whatever language they like, but there's still a bit of me that doesn't like it, knowing they've got no reason to talk ABOUT me, but knowing that it could be happening anyway. It's not that they're indian either, if it was a group of whites all talking in a foreign language it'd be just as annoying.