Why do some people discriminate and are prejudiced against others because they're different?

Obviously when they're little kids either their parents and/or friends are prejudiced and discriminate people who are different. And that influences these kids and they become prejudiced and discriminate people who are different because that's what they're taught. Until a certain age children don't right from wrong. One: the parents shouldn't discriminate and be prejudiced themselves. Two: the parents should teach their children it's wrong to discriminate and to be prejudiced. Three: the parents should teach their children people are people no matter what is their skin color which country they're from what language they speak etc. Four: the parents should only let their children be friends with nice children; never let them be friends with children who will teach them to be nasty to other people.