2 year old nephew calling me puta and puta madre

So I live with my boyfriend and his family. My sister in law has a 2 year old boy. Everytime he sees me he says puta and puta madre... bitch in English. He can't even say his first name! At first I let it slide or ignore him but I got sick and tired of him saying that that  I nicely told him to stop saying that. He continues... when he says that in front of his mom , my sil tells him to stop. But when he says it when his with his grandma (my mil) she doesn't say anything... idk if she completely ignores it or doesn't listens . I didn't know that him saying that will bother me so much!!!  I never did any harm to him.  What's the best thing I can do to stop that? Once my sil gets home from work today I'm going to tell her that his son constantly keep saying that and I don't see him saying that to someone else like if someone told him to call me that