To the above post (sorry, if a little off topic), but from what I've heard and a little of what I've observed is that since kids mostly parallel play until they're about 4-5 yrs. they're able to play quite well together despite gender differences. Granted, my girls' dearest friends are other little girls, but they have lots of boy friends, too and enjoy them. The boys kind of do their thing and my girls work them into their fairy-tale land.
All they have to do is say, "Prince, where's your horse, sword, etc?" and the boy goes running around the house on his "horse" and swinging things around....perfectly happy and the girls are MORE than pleased.
They, of course, have unicorns, not horses, but they all seem to have a GREAT time. Other times, boys really enjoy our play cookware too and enjoy making pizzas as much as the next guy (or girl). We also have our share of tools (dh is a carpenter) and the girls play with those things, too.
Sometimes, gender roles come out very strong if a boy is pretty rough and tumble and my girls are not at all....they're a little intimidated, but other than that...there's LOTS of fun years where there is no competition, no jealousy, etc. between boys and girls.