Obviously this could go one of two ways, so here are my thoughts...
Option one would be to go part time. I completely understand why you would want to be able to spend more time with your son and why your husband needs more time to work on his business. If your parents have a large enough home, it may actually work out fine. We lived with my parents for 7 months, it was only supposed to be 4, but things worked out differently. Everything actually went much smoother than I could have expected, and now I would have no problems having to "briefly" live with them again if push came to shove. It is a great way to pay down debt, and it would give your husband the extra time that he needs to focus on your family's business. The downfall of this is that if they were going to possibly give you a pink slip as a full-timer, your chances have probably increased if you go to part-time. Could you live and continue to pay down your debt on your husband's salary alone if you lost your job? Is your health care through your job, and if it is, do you continue to get it if you go part-time?
Option 2 is to stay put. Personally, this is what I would do for the next year. Is there any way that your husband could take your son with him to the office? Maybe he would be able to get more work done there? Even if you don't go part-time, maybe you could move in with your parents. That would help financially (and with the baby-sitting), but not cause you to lose any sort of income. You could always try it out for awhile and if it doesn't work, make other arrangements. You are right that this is a bad economy, and if your husband's business doesn't take off like you are hoping, what happens then? One part-time income is definitely not going to cut it. Like I said, if it were me and my family, I would not rely almost entirely on a new business that has yet to really bring in the money needed. Good luck in whatever you decide, it will be life altering in whatever you do!
P.S. You could always go part-time next year when, hopefully, the economy has rebounded some!