First things first:
There are too many checklists out there for telling you what it takes to be an entrepreneur, I am not talking about them.
Do you believe beyond criticism, reason and logic that you have what it takes to be an entreprenreneur??
If the answer is yes, read on. Be sure about it or you will regret this.
I think a good idea will be to take it slow. A phased migration over a time period of year+.
phase1:
For a few months at the start, maintain a status quo at current job just keep working right, but change your spending, living and saving habits.
Meanwhile prepare your family for the change, slowly. You have lived too long under the cozy umbrella of constant and guaranteed paycheck at the end of every month, that has to change over to a not so persistent income and amounting only to live well and keep the kids just happy.
Yes, as someone pointed out, convince and take along your spouse through this transition. Encourage her to take up a job if she is not already doing so.
Save money.
phase2:
Save more money :-)
Then move over to part time, at the same organization if they respect your work or some other organization. You can look at freelancing also, but that a different game, you will have to build that image slowly. Consider yourself lucky if you get good gigs at the start, which is not usually the case.
Meanwhile, during this 2nd phase transition, start developing a small fun/serious project or for open source in your part time.
As Gary[http://www.youtube.com/watch?v=EhqZ0RU95d4] says: work 9-5, come home, spend an hour with the kids and then 7-1 is enough time to do damage.
Second pointer will be start attending dev and entrepreneur unconferences[barcamp, headstart, etc], speak up, listen, you might make a few friends there who can appreciate what you know and vice versa. Do small weekend hackathons with them, to know them more. Not all weekends, some, spend the rest with the family.
Hopefully one of these friends will be the one you found your first venture with.
Zero on some idea that you are passionate about and a partner who shares the passion and vision. Starting out alone is not usually encouraged, but not ruled out.
Start developing a proof of concept and talk to people about it and get feedback.
Once you are sure that "this is it" and you have saved enough money for you and your family for 1year, or your spouse earnings will help in that.
phase3:
Get in ramen mode.
"""Startup!!"""
Now you are on a complete uncertain rollercoaster. No turning back. Remember this is a result of the "choice" you made not something that was forced on you, so persevere and may the luck with you.
You can shuffle a few things in the phases. :-)
Hope that helps.