K.N.
I'm sure this varies by state, but in Ohio a single mom can get all sorts of help, even if still legally married. Food stamps, help with paying child care costs, insurance......AND they will file the paperwork for child support. I left my abusive husband and didn't actually divorce him for 7 years due to the cost, received child support the entire time, well when he worked. It isn't easy to leave, I had just had my 3rd child when I finally got the guts to leave, no place to go, hadn't been allowed to work, no car, mountains of debt. That was 8 years ago, I now own a home, (which I bought before meeting my second husband), have a psychology degree and am working on my bachelors, and am expecting baby number 4.
having lived in San Diego, I know a lot of areas have decent public transportation, and any job is better than nothing. Call your local job and family services, start the paperwork, get some applications out, even if it's at mcdonalds or walmart, and start looking for a place to live, or even a roommate or family member to stay with. Join a church, and get involved, get the kids involved, and don't be afraid to ask for help. if you are strong enough to be surviving where you are you are strong enough to leave.