Hi, you shouldnt worry, it is natural for a boy to play with girl toys and girls to play with boy toys. Its a great balance and it will teach him to "play" daddy too, so no worries, I used to play with my dolls but I really liked cars casue they moved. My kids have gone through the same stages, even one of them used to sleep with a doll at night for awhile for comfort. My sons dad used to get mad and "hide" my sons doll cause he didnt like him playing with it, but my son would cry and Id find it from him, it was an incredible asset that he learned how "take care" of the doll, before I had his sisters, he seemed to be more gentle when they were babies. So really, dont worry about it..Let them play, soon youll be stuck in wondering why the kids dont want to play with their toys and want to play with cardboard boxes and 2 liter bottles..hehe..All normal..
At this age there really is little concept of boy/girl toys to a child. They are twins...they have been together since conception and he likes/admires his sister. I am betting your daughter seems to be the leader of the two. I think he just wants to be like his sis is all. I really would not be too concerned about it. It does not mean he will be gay or some how less masculine. I am a girl and loved tonka trucks but hated dolls...now I am definatly more girly for lack of a better term.