I'm sorry to hear about your situation. I know it is tough to try to keep cheering hubby on when things are not looking very great.
My idea is sometimes offensive to some moms here....(I have suggested it before and gotten nasty mom mail) but I feel it is worth saying again. I would stay away from all the MLM and "have your own business" offers. They sound great but most of the time you have to put an investment upfront and the only person making money is the one who signed you up. They prey on people who want something fast and at home...
I have done several focus groups for some of the companies around here. It is a lot of fun. You sign up, I am with Schlessinger, and they email potential groups to you for what they are looking for. If you qualify and are interested, you go do the focus group. I have made as much as $200 cash in 2 hours, trialed a razor study for 3 months (no razor purchases for 3 months!), babyfood trial when DD was a baby, interviews on advertising. It is very interesting. NOW, most of the time, they limit you to 1 study every 6 months. $200 is the most I ever made cash and $75 is the least. I justify the trip (gotta add gas and car expenses) by how long it is and how much I get paid.
A MDO program could also be an option for you to take your children along. Even if they do not have openings...they often need a substitute if a teacher is sick. I'm not sure how bringing your children along would work with subbing but the subbing could get you in the door.
Your errand idea sounds nice but take into consideration the wear/tear on your car and your expenses. Just make sure you can make some money.
Sell things on EBAY or Craigslist.
I hope there are a couple of ideas that help you here.
Best wishes to you and your family.