It's relatively easy for a parent to work 12+ hours/day as long as there's a spouse at home who can dedicate his/her life to the children and household.
So, as a woman in startup tech, if you choose to have work and family life simultaneously, it means finding a partner who will do that (is willing and financially stable), and/or outsourcing a significant portion of your childcare to family, nannies, etc.
Unfortunately everything has a price - spending more time at home has a price (earning less money with the startup?), spending more time at the office has a price (no kids). But you have a choice.
In another comment you said that your particular startup requires the long hours. Maybe you could restructure the startup? Maybe you could spend some money on employees? I don't know - but overall I don't see how you being a woman makes it in any way special. If anything, you have more choices than men?
And the man working long hours also might not benefit from his children much. Except maybe later in life, when they are older and he works less?
I didn't want to come across as harsh. I just suspect that in hindsight it is common to wonder what for did one sacrifice family and children? I am 37 (male) now, and I don't really have a strong inbuilt desire to have children. But one could just go for it and see what happens? If not now, then when? Other things are probably more easy to delay.
I admit that I am also becoming cynical about the traditional roles. I am not that thrilled about having to provide as much money as possible to compete for child rearing women. It may still look as if men have the better position in society, but it doesn't really make much sense. Men don't have any bargaining position at all. They are 100% replaceable (sperm is cheap) - so struggling to be as successful as possible financially is pretty much the only option. Men have to take the risks - women pretty much can opt to take them for fun, or not. More or less, at least...