You may be right modeller, and certainly over a social change as big as this one could be we need to be sure that the children involved are not affected. However again it may just be a short-term thing -- were not children of mixed race or mixed heritage bullied in the past? Some still are, probably.
There are several stories going around the internet, if you look, of young children reacting with complete indifference to all sorts of things that some adults have a problem with -- gay parents, transsexuals, people with disabilities and so on. With care, children can very easily accept what we might think of as different. On the other side of the coin, of course, children can also be extremely nasty, so some of those with a different background of any sort will undoubtedly suffer.
I don't think that's a very good argument against change, though, since it takes nothing at all for some children to be mean. Glasses, spots, strange choice of clothes, you name it.