When my kids aren't SO little I plan on garage "sailing" all summer for really cheap and well maintained children's clothes and maternity clothes. We have GREAT garage sales in our area, not all of them offer very cheap clothes, but some do - 50 cents or a dollar per item. I'll put together matching outfits and sell them at Children's consignment sales twice a year - it's $12 to list your clothes and then YOU price them at whatever you like and you get 70-75% depending on if you volunteer or not. The clothes sell for $4 or $5 an item - more for an outfit, especially name brand. The other option would be to put together "lots" of clothing in one size and sell them on ebay. Very cute lots of clothing (maternity are SUPER popular!) with EXCELLENT pictures sell for great prices. Draw backs are you have to "invest" some money and keep these things stored somewhere. I would freshly launder and if possible iron everything as it brings the price up when they look crisp - this would be a great idea for a young girl to do, as with a minimum investment $50? she could make a nice little profit.
Obviously this may not be a sole source of income, but a little extra that could help add some dollars to the bottom line.