I used to think this way too. I would tell all my friends that if a boat were sinking with my wife and small children in it, I would save my wife first as we can always make more children. This is logical and makes sense to me. Then I had kids. It turns out that many of us are "genetically programed" (or however you want to phrase it) to save the kids first. Our minds don't always seem to work the way we want them to. I can still clearly see the logic of saving my wife first and would agree that this is the proper course of action but my brain simply won't allow me to do that. I am 100% sure I would save the kids first and let her & myself die. Wierd huh?
Of course I still believe strongly that if you are going to have a kid then you should also have redundant back-ups (more kids).