Have you tried ThredUp?

[kctmom]

Thredup lets parents across America exchange boxes of clothes that no longer fit their kids for stylish ones that will - all through an easy to use online interface, with a group of favorite senders, and from the convenience of home. Unlike typical "swap, buy or sell" sites out there, thredUP eliminates critical friction making it much more convenient for the average family. On thredUP there is no bidding, no auctions lots, no rifling through consignment racks, no bartering and absolutely no trips to the post office. It's the perfect solution for busy parents looking to save time and money. Plus, it can be kind of fun!

Like Netflix, you can choose a box of gently used clothes you'd like to receive. You pay $5 + shipping and you agree to list a box of your own child's outgrown clothes. The box you picked is immediately sent to you by the member who listed it. Then, similar to eBay, you list a box of clothes that your child no longer wears. When someone picks your box, you send it free of charge (we even have the USPS pick-up the box at your house). We manage the quality control and review process and take care of all the details to make sure you get a quality exchange.

Kids Sizes Newborn to 20!

If you join using the link above, you get a 1 month PRO memberships. Its important that once you join you complete your sign up checklist. A PRO member has access to exclusive features on thredUP. This includes more detailed box listings (including brands, types of items, notes, etc.). PRO members can have an unlimited number of friends in their "Inner Circle" and can add multiple profiles to their account. PRO members also get access to special promotions and giveaways.

I personally have traded several boxes and have been delighted with what I have received.

[concernedshopper]

It kind of bothers me that you have to pay them an additional $5. Guess I'm spoiled by paperback swap where it's a similar concept but there is no additional fee, it's just postage.