Children swearing

So I had a slight argument with my brother recently as he was telling his 2 year old to tell me to f**k off..I said that I think it's very wrong encouraging his child to swear,he says it's only allowed at home and that I am a snob...I have 3 children & I have never heard them swear (im sure they have) as I try to teach them that it's vulgar to constantly use bad language..I'm just curious on everyone's opinion is it ok for a child to swear or should you teach them it is wrong?