Used shoes — buying, selling, donating

As parents quickly learn, small children's shoes are outgrown while there's still a lot of life left in them. Depending on habits (at one point, my daughter was using the top of the toe as a brake when tricycling, ruining shoes quickly) and frequency of wear (during the school year only two pairs of shoes get much wear) the shoes might be cosmetically perfect or imperfect. What do you do with your worn shoes? I often fear some shoes aren't pretty enough for something like Goodwill, which resells them, but they're still really solid, and I hate to think of them just winding up in a landfill while some kid somewhere goes without shoes. If you buy used shoes, what do you look for? If you sell, where do you sell?