Sozzled and BabyBarrister,
I had posted earlier (and another poster has has well), that research shows that children by the age of three not only notice colour differences, but already start attaching value judgments to these.
Why do children at the age (black and white) select white faces as being more desirable than other races? Where does prejudice come from? First call is family. But it could equally be peers at school, books, media (e.g., only see white faces in powerful positions), jokes about races, using terms which are patronizing about others e.g., referring to a whole group of people as "chocolate face, or brown skinned", while referring to people of your own race as individuals, e.g., Aunt Sally, Peter's mom etc.
Studies point out that if no one talks to the child openly and frankly about prejudice, a child could grow up thinking that this is the way it is supposed to be, and that people who have been discriminated against deserve this treatment because they are inferior in some way.
It seems that children who have poor self-images are more vulnerable to developing prejudices. They may try to bolster their own worth by finding a group of people whom they can put down. An insecure child might think, I may not be very good but I am better than those people
So many people who are good for nothing and moochers in society are racist, because it gives them a psychological boost to put people down and feel important and powerful.
So why wouldn't you ask your child frankly, "why don't you like black men" and have an open discussion on race and prejudice. Same for the Chinese school children example.
Why do we assume that children age there and four are 'innocent' and not capable of absorbing prejudices? Of course they can, and if no one talks frankly and openly, they will just continue having these prejudices. BabyB, for example, your child may have black friends, but may still feel 'superior' to them and it could make him feel good about himself, an 'alpha male'. Why don't you have a frank chat and see what is going on?