I have noticed - in an extremely unscientific survey - that most of the white children I know have only white dolls. I mentioned this to someone recently who wondered if all children tended to have dolls that looked like them. In my (again, very unscientific) observations, however, children of color (in the US) tend to have both dolls that look like them and white dolls. This makes sense, as there is a wider variety of white dolls than other colors, of course (in the US).
When having these conversations, I can't help thinking of the doll experiments performed by Kenneth and Mamie Clark in the 1940s. These were the experiments cited in the Brown v. Board of Education case that eventually led to the desegregation of schools. The experimenters provided children with two dolls that were identical except that one was white and one was black. They asked the children (ages 6 to 9) things like "Which doll is the nice doll?" and "Which doll would you like to play with?" They also asked which doll was ugly, and which was bad.
Sadly, the results are predictable. Most of the children - black and white - said that the black dolls were ugly and bad, and that they'd rather play with the white doll, which was nice, good and pretty. This was used as evidence that segregated schools hurt the psyches of black students.
My niece is an example of how kids start out before they learn that they're supposed to think a certain type of person is pretty, good, bad, nice, etc. She is a (very) white toddler, and has a white doll with red hair, a brown doll with black braids, and several beige-ish tannish dolls that are ambiguous. She loves them all and carries them around in the crook of her arm. She likes to comb their hair and was confused about the fact that she couldn't comb the braids, but it didn't affect how much she liked that doll. She still has no idea that there are different races and ethnic groups, and - although I often wish she could stay in that phase - I do think it's possible her to learn the differences without assuming that one group is better. And, as silly as it seems, I think that having dolls that reflect the people in the world is a good first step.