Unit 11- Social Psychology

So my 6 year old son is going through some problems in school that I learned about in this unit, so the other day my son came home upset and I could not figure out why. So after about 3 days of this happening I finally sat him down and asked him what was wrong, he tells me that his best friends parents told him they could not be friends anymore because he is white and his friend is black. I was blown away by that to hear a 6 year old tell me his friends parents told him that prejudice was okay and that he cannot be friends with someone who is not of the same race. to me this is very sad and hurtful I told my son that some people are just like that and the only thing he can do is be nice and friends with everyone.