Was I wrong to intervene?

Ok, so I have 2 children a 3yo and 8 month old, and my cousin was telling my new baby that he was so much cutter than his big brother and I told her not to say that because my 3 yo understand what that means. And her mom was like that's ok for them to say that because and everyone says that about new babies and that I need to start teaching my son how to have thick skin because we he gets older many people might tell him he is not so cute.