First of all, don't panic or overreact. We all live in a country that is having its own struggle with racism and bigotry. Yet children must understand that ethnic or gender slurs or hostile remarks about another's appearance or disability are not acceptable. It hurts his feelings. At the same time, victims of such attacks should have ample opportunity to protest and speak up for themselves.
Some people feel ill at ease when children point out differences they perceive in other people.
While these are not easy or necessarily comfortable situations to confront, they can provide excellent opportunities to clear up confusion and provide accurate information that is vital if your children are to develop healthy attitudes about race, gender and identity. Be sure to provide your children with access to a wide array of multi-cultural materials on a regular basis. For example, in order to generate positive feelings, you can offer paints and crayons in a range of skin tones, and books that show diverse cultures and counteract gender stereotypes. But even though materials are important, what really matters is the respect you model when dealing with other adults and children. It's also essential to emphasize that no matter what culture one is from, all children share common needs and characteristics.