How do I respond?

Okay so I’ve noticed the women in my family repeatedly make comments about my son touching their boobs. Specifically when they pick him up (he’s 1) he’ll put his hand on their chest, which is a natural reaction to me. But they’ll make it joke and say he loves boobs, or he’ll be a boob guy when he’s older. I’ve said “he’s a baby, he doesn’t understand” numerous times, but it must be going in one ear and out the other. I’m sick of it tbh, and now that he’s starting to understand things I don’t want him to pick up that language. How do I seriously tell them to knock it off?