How to tell my coworkers to shut up?

I have a mixed son. Sometimes people at work start talking about black people in front of me. How can I tell these people to shut up in an assertive manner?

Tell them that what they are talking about offends you. Explain why if you feel the need to. I think sometimes people dont realize what they are saying, or speak without thinking because they dont realize the extent of their words. I know it is hurtful for you to hear, but try to be as nice about it as possible, to keep some respectful level with your coworkers. If they continue, leave when you hear a topic like that come up. Have not part in it. You shouldnt have to sit there and listen to that. If they respect you then they will stop doing that in front of you!

u needa tell them that yure son is black and if they want to b racist not to do it in front of u

The question is that what they tell about black people. If that is really hurtful you may interrupt them independently on your mixed son. But in the life everybody should endure some notes, even if that are not 100% friendly. The proof fo the quatily of your mixed son will be his life.