I work with young children and their parents. I have come across this kind of thinking before and the latest example was today when I explaining to a dad how to help his 2 year old son develop his pretend play skills by using dolls/teddies and a toy kitchen:
Dad: Dolls?????????? 
Me: You look horrified (smile)
Dad: Well I just never would have thought of giving him a doll
Me: Because he's a boy?
Dad: Well, yeah
Me: Little boys and girls both need the same opportunities to learn to pretend play etc
Dad: So it won't turn him a bit.........?
Me: Turn him a bit..........?
Dad: Oh well I guess he's only young yet....
So obviously in my head I'm saying FFS! What I really want to say to dad is 'oh you mean will it turn him gay? Oh I see! Well rest assured that there is nothing that will turn him gay - if your lovely boy is gay, then he's gay already!' But I had a feeling that would not have ended well.....
Almost the most depressing thing about this whole depressing episode is that this is a stay at home dad! I did point out that he's a man, and a dad, and that he takes care of his baby, and that there is nothing remotely weird about that, and so what could be wrong with his son pretending to do the same thing with a doll???? But you know when you just know that it's going to take a hell of a lot more to change someone's long held prejudices beliefs.......
I feel very strongly about challenging this nonsense but I also need to keep the parents on side. All thoughts and advice would be gratefully received