When is it a right time to teach a child about racism? What would be considered age appropriate?

I have a 6 and 4 year old and we live in a pretty diverse neighborhood. His class has asian kids, white and black and a few hispanic kids. My children are a mix. They're hispanic and white but got mostly my husband's features so they just look white. So i was having a casual conversation the other day but it soon turned awkward and it stuck with me. Mostly because of what the other person was saying. I said that my oldest had learned about Dr Martin Luther King in class and was starting to ask questions. I said i was going to teach my children what happened in the past but also that anyone could be racist and that its wrong. Because racism is basically hating another race and thinking your race is the better one. ..Right? Because just as there are white people that hate black people. In my life i've encountered several people saying that they openly hate white people. Videos on-line about black people who want to kill white people etc. Just a few months back i remember there being a post here (not sure if anyone will remember) about a white momma who's small child (3-4 years old) walked up to a black woman and mentioned an innocent observation to the momma that her children probably are black like her. Which set the black momma off and insulted the white lady and her daughter. And it was just a mess on the posts between people defending the black lady and others defending the white lady. I honestly thought the black lady was probably racist herself. My husband who is white works with teenagers and he's met a few black children who will openly insult and disrespect him, and ask for another black person to help them because they "hate white people"I just think racism comes from all sides and from ignorance and people not caring to get to know one another and show empathy to their neighbors. But this person just told me "Black people CAN'T be racist, they CAN'T". I hope this doesn't become too controversial. Am i wrong here? I just wanted to know what other moms are teaching their children. Are there any books out there good for a 6 year old to read? via /r/Parenting https://ift.tt/2GAF3sZ