You would teach a 5 year old about sharing, but not sharing with others that look different? Racism is wrong because there is only one race. Pretty simple (I went to majority black schools growing up and majority of my friends were black because of it. I never saw them as different because they aren't). Sex on the other hand is something more of an age related thing that everyone is going to have to face growing up. It should be taught in the early teen years that it isn't wrong, dirty, or for everyone (asexuality is rare, but shouldn't be considered abnormal)