I have 4 kids, three girls and a boy, and they play with other kids their ages, so I have a fair amount of experience with little kids. There are corner cases where you can't tell what's nature and what's nurture, but you haven't really watched little kids if you haven't noticed that little boys (i.e. 2 year olds) bounce off walls much more than little girls, and there's no realistic nurture mechanism for that difference, at least among my friends and neighbors kids. More or less none of us have televisions, and it's too young to be training them at sports (or at least I haven't witnessed any of the parents doing so).

Legos, on the other hand, seem to be nurture: my daughters play with legos more days than not, and we don't have any pastel bricks.