Substitute teaching will have you home more or less when your kids are, especially if you sub at their school. In Ohio you just have to have a bachelor's degree, in anything (and I mean ANYTHING) to sub.
(I sub but do not have a teaching certificate, and am contemplating going back to school to get it, so I read your letter with especial interest. )
If you sub at other schools and you won't get home exactly when your kids do, a child care option is a must--e.g., go to the Smith's house until Mom is home, or have Grandma meet the bus at your house, or....you get the idea. Ditto for the a.m. if you must leave earlier than your kids. (I bless my neighbors for waking up as I banged their door at 6:50 a.m. so Philip could catch the bus at 8:15 with their son!)
The good things are that you can say "no" if your kid is sick, or you want to chaperone the field trip. And you are not stuck with a horrible class day after day if you don't want to be. If you hate routine, you'll love subbing because every day is a new adventure!
The downside is that it is not steady work, you never know how many days a week you will work. But if you have a part time job a couple evenings, or part of a weekend (think "Daddy-kid bonding time" here), you could throw all your subbing wages at your debt in addition to the "regular" part-time stuff. Whoever said double up payments has the right idea (but you probably knew that already! even if you just pay a little extra, it helps, assuming there is no pre-payment penalty)
Could you start your own business and work out of your home? Would you be comfortable doing in-home child care? there is always a need for that.
What about contacting the temp agencies and seeing if there is anything they have that could be done from home on a computer, e.g. data entry? I have heard that there are customer-service people who work from home answering phones, but I don't know how to go about finding more info.
Could you consult? Do party sales (Tupperware, Pampered Chef, etc)?
Make a craft and sell it? Cook or sew for other people? grow and sell fresh veggies?
Sell on ebay? Run an errand-running service for parents who work full-time? Do a garage-sale-shopping service for same? (you get a list of what the person wants, and the max they are willing to pay; if you find it for them they pay you a commission)
There is a company near here called Comfort Keepers, they provide in-home services (cook, clean, shop, errands, companionship) to elderly and disabled. I know of someone who works for a company like this who can only see one client per day because the family only has one car and she has to work around that; so maybe such a company would be willing to let you work "Mom's hours".
Free-lance writer or newspaper columnist? on business topics?
Teach a business course to home-schoolers?
Church secretary? I know a number of churches that only have a person in the office half a day.
For tips on curbing expenses check out the Tightwad Gazette books at your library.
Network, network, network.......let everyone know you what you're looking for, who knows, maybe there is a company who needs your skills/knowledge but can't afford someone full time???
Finally , don't beat yourself up. You make the best decisions you can, with the info you have at the time. I believe that nothing you learn is wasted. It will all work out, probably with a lot of little things adding up rather than with one "magic bullet".
You may not fully utilize your degree until your kids are much older. I say follow your heart and be there when they get home from school---you have your whole life to work, they are only little for a short time. Send me a message if you want to talk some more.
Sorry to run so long, hope some of it helped. Good luck and let us know what happens
K. Z.