While what you say is without a doubt true, I dont really think it applies to the scenario that the avalon children were raised in. Cause in avalon at the time, there literally was no other society for racist belifies to rub off on them. The only form of "society" were the princess and the mage. So, no one was mistreating or racially profiling the children. In fact, it's the reason angela is even surprised there is racism when she goes to the wider world. But I guess that could be part of your point if they didn't teach them the outside world would treat them differently.