in-laws to watch their language

How do you politely tell your in-laws to watch their language when your little one is around? My brother in law and father in law curses a lot. My father in law particularly. He curses in spanish and filipino as if its his spoken exclamation point (he's half spanish)! My husband and mother in law already warned him multiple times for my 20 month old has this awesome skill of copying and recording everything in an instant. But it is part of his system he cant seem to control it. My baby once cursed back! Help