Sorry you are going through this..
Start by filing for unemployment.
Then go to Thrift shops and Goodwill to see what you can get there for less money...
Go to your WIC office and see if you qualify for WIC..
I will assume (don't like to do this) that you are married...see if your husband can pick up a second job.
If you own your home - see if you can refinance your home and pull money out to help you out...
If you have credit cards - stop using them...you are only spending money you don't have....go to your library and borrow books by Dave Ramsey or Suze Orman - and get your finances in order...
With 4 kids - you may have to be a SAHM in order to stay afloat...I don't know how old they are....
Don't worry about winter clothes TODAY...you can go to K-Mart and put them on lay away - that will help you get what you NEED and pay CASH for it over time instead of all at once...
If your kids are in private school - sorry - take them out and put them in public school until you can afford it again...don't want to do that? call their school and find out if they have a scholarship program that you might qualify for instead of pulling them out...
You won't know about these things until you ask. Write down a list of things that you NEED to do...don't try and take it on all at once....you will get so overwhelmed that you will make yourself sick...
So start with unemployment
then call your mortgage lender, if you rent - tell your landlord what is going on...
if you have a car payment - see if you can sell the car and get one that doesn't require payments....
go through the house and get rid of everything you haven't touched in six months...list them on craigslist or ebay to get money in the door.
Get rid of phones that you don't need - and start living with necessities instead of wants - distinguish between the want and the need...cut cable out completely - start using Netflix or Blockbuster...
Cell phones - get the bare minimums in minutes or find another carrier that can fit what you need.
Make weekly menus for meals - this will help you shop more efficiently. If you can order your food on-line - do that - it will save you a ton of money because it stops the impulse buying...
Clip coupons...
Call your electric, gas and water company - find out if there is a flat rate program you can go on to help keep your finances in order...
Employers cannot keep from hiring you because you are pregnant...make sure your resume is put together and start looking for jobs...there are real jobs on craigslist...look there...you didn't state why or how you lost your job last week and I don't know what you do - but get the word of mouth out as well!!
GOOD LUCK!!