Having grown up in a 2 girl family and then having 2 girls myself, when my first DGC turned out to be a BOY I was somewhat surprised. It took a bit of getting used to (fell victim often to the deadly accurancy of his 'pee in your eye' technique) and the sheer size and weight of him came as a shock. He was followed 6 months later by DGD1 and his wee sister, DGD2, came along after a couple of years - giving me a fascinating opportunity to compare both genders, being brought up virtually identically. The similarities vastly outweigh the differences. All 3 love music, stories, dressing up and performing and show little interest or skill at sports - not at all surprising in our family which is full of singers, dancers, musicians, film makers. All 3 play with the same toys and enjoy computer games, but then differences start to appear e.g. GS will invariably choose a fighting, demolishing or agressive computer game, whilst the girls like games which build things, make cakes, furnish or dress up. Woody and Jessie from Toy Story are great favourites but again our boy makes them fight each other while our girls tuck them up to sleep in a shoe box. We noticed from a very early age the STICK effect - for Grandson all sticks are weapons, swords, guns - our DGDs use them as musical instruments, cutlery, magic wands, or put found sticks in the log box.
An anecdotal exception: - DGD2 found a small wooden cross with a pointed end and a poppy attached (sent to us by Earl Haig Poppy Fund). She considered it carefully and then announced that it was a GIRL's SWORD because it had a flower on before discarding it, uninterested.
GS uses a torch as a Death Ray, the GDs think they are sunbeams. They only other major difference I see is in attachment. When GS is tired or upset he wants Mummy or Granny, GD2 is very much Daddy's or Granpal's girl but then DG2 shows no preference really, is equally cuddly with all. I think there are really 3 influences - gender, personality, upbringing/expectations and the greatest of these is - IMVHO - PERSONALITY.