You can do both (as I'm doing), but not exactly with the same ambition. I'm more of a lifestyle entrepreneur, growing the business slowly, managing my hours and spending some some great time with my wife and baby.

If you're aiming for the VC-backed billion-dollar startup with 80 hours work week, surviving on pizza and coke... Then your setting yourself for a failure as a dad/mother if you try to have a kid at the same time.