ThredUp is a site where you can exchange boxes of clothes that your kids have outgrown with other families.
Here is an excerpt from their site:
ThredUP is where America’s busiest parents exchange boxes of clothes that no longer fit their kids for stylish ones that will. We coordinate swaps among a group of your closest friends or connect you with thousands of families nationwide. There’s no bidding, no auction lots, no rifling through consignment racks, and absolutely no trips to the post office. All swaps are done online, with scheduled home pick-up and delivery. ThredUP is the next generation of swapping – a kids clothing revolution!
Right now when you sign up you will get your first box for FREE! After, that you’ll only pay shipping for each box of clothing that you swap!