2 kids. 7 year old and 3 year old. Started my current company when kid #2 was born (maybe not the recommended course of action for everyone, but I survived).
People ask me what my hobbies are these days it's pretty much (1) the kids and (2) the website.
In fact, I'd say the website is almost like a 3rd kid. Once that thing went public it was 24/7 just like a kid! And it even wakes you up at the least opportune times like a kid.
But I do find that with kids I'm forced to be resourceful and disciplined. I sleep less and make do with what little "me" time I have to get things done. I also find that I'm forced to prioritize things more (triage becomes really important when faced with greater time constraints).