Steve Blank had a good post about this, if you want some perspective from someone who has actually dealt with these issues:
http://steveblank.com/2009/06/18/epitaph-for-an-entrepreneur...
http://steveblank.com/2009/06/18/epitaph-for-an-entrepreneur...
As my daughter slowly grows, I see clearly that a neglect of not spending enough time with her for a longer time can't actually be compensated later on, and that could only create regrets when I'll get older.
My experience have been so far that family/career can be balanced, since it is always possible to squeeze out more time for work by getting up sooner, stay awake longer or give up some personal leisures.
That has made a huge difference to what we can both get done in a day - no need for long commutes (previous role had a commute of 2.5 hours a day) or school drop off and pick ups.
Its seems like its only now that I've gotten as close and comfortable with my first as I am with my second child.
I'm learning first hand that babying a startup while starting up a baby is an awesome challenge. Actually the two don't differ much in mindset - total dedication is the key.
So I try to do one thing at a time - and do it wholeheartedly. It's trickier then it sounds, requires constant tweaking, but pays off in dividends.
(I find that this related HN post deals with some of the practicalities mentioned above - "Self-control is a limited resource, use it sparingly" http://news.ycombinator.com/item?id=1207136)