On my end, becoming a dad didn’t make me less ambitious, just more focused.
I was vp of engineering at a Series A startup when my kid was born. It was a challenging job, but one that felt increasingly devoid of any meaning for me (maybe also because I'd been there for 5 years). I was compensating by working on side-projects at night and on weekends. I even wrote a novel that took me 4 years to finish.
Then my son was born, and nights and weekends disappeared! Suddenly, all my non-father activity was dedicated to a job that was boring me more and more. So what did i do? I started a company, so I could decide what to work on during the day!. Basically, I took a side project and put it at the center of my working life. Now my days feel rewarding enough that when I disconnect, I can completely devote myself to my son and my wife and ignore everything else.
Of course, I don’t have side projects anymore. I barely even have hobbies: I completely stopped watching movies, which used to be the love of my life. I read books before bed and on the subway, and work out occasionally to stay sane. My life = my startup, my son, my wife. That’s pretty much it.
But I feel much more balanced than before, when I was always chasing something.