> I make $100,000 / year at my day job and have a wife and two kids. What could I do to make the leap and feel secure at the same time?

Does your wife work? Could she potentially be the bread winner when you don't have any projects (say for a few months?).

You can make a lot more than USD 100K per year through freelancing. Of course you could end up failing as well. There's always a risk involved.

I'd suggest talking to your existing client(s). Are any of them offering you a long term projects?