I enjoyed this story for many of the reasons already mentioned--interesting kid POV, but also interesting kid-mom dynamic, and interesting playground class dynamics (rich vs. poor).
But like many listeners, I feel like there's some really interesting politics going on here, both economic (what happens next time the supply runs low, how long before this new crop of charms gets snapped up by existing or new hierarchies?) and environmental (the charms are a finite resource on one hand, but, without any particular husbanding or care, they are also an infinitely (as far as we know) replenishing resource).
I also wonder if there are any anti-charm people out there in this world--people who think absorbing charms is devilish or simply an unacceptable change of the self. (Like, wasn't there a "laughs easier" charm? I can totally imagine someone who was told by their therapist to get one of those charms to cure their depression; but how many "I don't want to take pills, this is my sadness" people are there (in fiction, at least)? And that's just one example.)