My sweet three year old son is picking up old-fashioned gender stereotypes from his grandfather, whom he reveres. What can I do?

My son is three. He spends a portion of each weekday with his grandparents while my husband and I work.The other day he was explaining his “dinkie” configuration to me. They were arranged by twos and he was pointing to each and saying, “this is the boy, this is the girl,” etc. That was all fine. Then he pointed to a truck and said, “this is a girl... “ then corrected himself: “no wait. Girls don’t drive trucks! They just drive them in the ditch!”I was shocked, and 100% certain this idea didn’t come from our home. I asked him where he heard that, and without skipping a beat, he named his grandfather. I did what I could to dispel that myth, also telling him he shouldn’t believe everything his grandpa tells him, as he likes to joke around a lot.I was sort of fuming that my FIL is putting these ideas in my son’s head. I couldn’t stop thinking about it. The next time I saw my FIL, I brought it up casually. My tone was light and playful because I wanted a confession, not defensiveness. Anyway, he denied it entirely. I should note that there were other people around listening in, and admittedly that wasn’t the best time for me to address it. Perhaps I would have had better luck if it had been a private conversation. But like I said, it was weighing heavily on my mind.In the next couple days, other stereotypes emerge from my son, and again he points the finger at his grandpa.One thing he likes to wear sometimes is a little flower keychain on his belt loops. He was asking for my help to put it on. Then he said, “but flowers are for girls.” Again I dismissed that, and luckily he accepted that and still chose to wear it.Another thing he said, in response to being told he was “sweet”, was that men aren’t sweet. Only girls. (When we pointed out that he is not a man, he argued this. He’s convinced he is a grown-up, again I think because his grandfather “goes with it”. Whatever. I don’t care about that as much as the gender stereotypes.) I told him that sweet men are the best, and his father concurred, and goddamn I hope I can still raise a sweet boy despite everything he hears to the contrary.Despite how mad this has gotten me, I have an excellent relationship with my father in law. I don’t want to immediately give an ultimatum. My FIL is crazy over my son and misses him terribly when he’s not around. They both love spending time with each other. But I need to communicate to my FIL that we try to raise our son without these damaging stereotypes. No, I can’t raise him in a bubble, but he’s too young to have these stereotypes propagated around him- and by his family members of all people!Now I know how kids can make up stories and stuff, but I trust my son is telling the truth in this situation.Any tips on how to handle this would be greatly appreciated. My in-laws offer free childcare (and would refuse payment anyway), so there’s the caveat in this whole thing. They would also be very upset to lose this privilege, so again, my goal is to work this out, not remove him from their care.Thank you. via /r/Parenting http://bit.ly/2w7M5yx