Parenthood is kind of a good rehearsal for founding a company: you won't sleep much, you're very emotionally invested, you're on the hook for everything, and boy is it hard without the right partner.
And quitting your job to try a startup is fraught with a whole new peril -- you've got a family to feed!
I can imagine starting a part-time lifestyle business and taking it full-time if it ever became successful enough, but never a full-on work-til-you-can't-work-anymore startup. People who can do this after they have kids have my utmost respect, but I genuinely don't know how they can do it.