DS is nearly 4.
Asked for a water pistol this morning, said it was "only for boys". I told him that girls could have water pistols too. He argued with me, saying that "Elliot at nursery" had told him they were only for boys, but girls could have pink ones. 
He's come out with this a few times (not helped by Grandma telling him that Peppa Pig was for girls!) and I always explain that boys and girls can do the same things, but he seems to favour the opinions of his 3 year old peers than me 
Any ideas?!