And that's when it occurred to me that maybe I was looking at regifting way too narrowly, as a way to manage down the social convention of gift giving. And that's fine. Your kid gets yet more toys they don't need, or gets duplicates, it seems like no big deal to be grateful--and then to pass them along when you think there's a better chance of their being used and loved.
But the real power of regifting might lie in teaching a kid to not only think of her friend, and give something her friend would like, but also to give something of her own to her friend. It could make the gift--and the gift process--more meaningful than, "Here's something my dad picked up for you at the toy store."