Children of modern parents don't show stereotypical differences between male and female?  Which ages are you talking about; the ages from 0 to 5 where males show signs of aggression and competitiveness over the more sedentary, gentleness of females?  Or the school-aged children where the masculinity of boys has been relentlessly repressed making them seem more like girls; and forcing girls to engage in competitive sports to make them act more like boys?

Funny that as puberty approaches, boys and girls typically revert to their sex-based characteristics.  Hormones are a powerful thing.