Yes, it changes absolutely everything. I'll also say it generally makes life better, you can talk about work/life balance before a child but it takes on a completely different meaning. It's not more time at the gym or more xbox or more time outside that you're balancing work against, it's more time with your child. There simply isn't a comparison. Something else, I think I was a great deal more selfish before hand, I didn't think it at the time and I never intended or wanted to be selfish and I don't think I'd have described my self as such.
As for work and work related things, it provides an incredible filter. I've always had too many ideas and had to somehow filter through the bad ones but try to honor every idea to see if it's bad, you simply have less time to screw around and you either become more efficient and effective or you become more mediocre. You either embrace that or you fight it. Where as before, I could spend 6 hours on a Saturday morning just screwing around, maybe learning a new tool or language or something, now I've got maybe 1 hour on that Saturday and I have to make that time count more. I was maybe more oriented towards just trying stuff and seeing what happened, now I have to be a bit more thoughtful and it's not an entirely bad thing, when you just experiment and try you kind of don't excercise some parts of your mind the same way. Some of the screwing around some how seems more satisfying now when you can actually do that.
In some ways, it redefines "success." I've had mentors and peers that have sort of fallen in to two camps. 1 camp says entrepreneurship is a young man's game, it's countless really long weeks, doing every job you have to to get the company to work, you might just have to grind, at some point you either want to have a life or burn out and then you're done. You might have to choose between a marriage and your buisness. The other camp insists that it's better to have your support structure in place, how can you possibly start and run a really good company if you don't have support at home? That support is a loving family. A child almost forces you to be in the second camp or give it all up.
Now, personally, what's interesting is that when I was 23 or 24ish it seemed like there was this spectrum of success that went from Bill Gates style billionaire down to being some hired contractor that did coding jobs to pay the bills. Ultimate success would have been to grind out a decent company, sell it for a billion dollars, take some time off to do stuff that "mattered" (even though I was probably too selfish to really do it) and then try to do it again. Now, building something sustainable that I love is the goal, something that allows some balance, something that would be really hard to just walk away from for a pay day. Something that allows my co-workers and employees to live satisfying lives, start families, and have some balance too. Oddly, that goal seems much better to me and I think it is radically easier to achieve.
That is of course after that first rough year to 2 years.... Even if you sleep, it's just a lot to digest having a little human that completely loves you and depends on you for everything.