Oh yeah, gender is definitely important and I believe, genetic. However, it can assign in any way in any combo to the physical sexes -- nature is certainly polymorphically perverse. I loved "little girl" baby dolls and pink and yellow blankets, but I'm definitely hetero, though I can notice a good looking man without discomfort, unlike may guys I know. And most gay guys I know knew they were gay from a very young age.
A guy like Eddie Izzard must get so many questions -- feeling comfortable dressed in women's clothes but definitely being hetero. But to me its just nature creating every potential combination, some of which will be "successful" and others not so much. Its really wonderful frankly, especially because as human beings we don't have to struggle for survival, and most of these rare adaptations can flower and grow without nature destroying most of them.
As far as trying to mold a child of one sex as the other, that sounds like child abuse to me. Letting a child express and discover who they are in a safe and non-judgmental environment is the job of a parent IMO.