I had a garage sale last year, put out lots of kids clothes, just marked almost everything $1 and sold a lot of stuff. My neighbor had twins and did the same thing, just had bins of clothes and said everything was a $1, and if someone wanted to buy a lot, then she made them a deal. You can advertise your garage sale for free on Craigslist. Get a friend to help you run it - maybe another friend who needs to purge her closet and you both make some cash!
Also, a friend of mine hangs all their clothes - everyone's on wire hangers like you get at the cleaners, so you can fit a lot into a closet, then you can see what you have. She had 2 boys, hung all their tshirts, only things that went into drawers were socks and undies and shorts.
Get your kids to help you sort the bags of clothes by size. My 7 y.o. helped me sort 3 huge bags when I was preg with baby #2 - she sorted by size and helped put like things together - onesies, sleepers, pants, shirts, etc.
I also made some money selling at a consignment sale - "Just Between Friends". It took a couple days to sort, tag and take to the sale, but I made $77 after expenses, which paid for the things I needed for my baby. Look up "consignment sales" for your area.
Ask your friends for help - when I was 5 months pregnant and moved out of state, I had a friend come and help me purge my closets for a garage sale, and told her she could have some stuff for helping me out.
Good luck!