Now that would be a good idea that I am sure a lot of children would like. In fact I think there already is a few reality shows mining that topic.
Zwaggle is another sort of parent exchange. I have been intrigued with the general Free movement -- I mean why not just give it away? Imagine what it would be like if you had a close group in your area that freely exchanged hand-me-downs without any need to barter for what you get back in exchange. Just give in good faith. After awhile doesn't everyone out-grow everything (other than their loved ones, family, and friends that is).