The fey who reside in this area are well aware that they are outclassed by many larger and stronger creatures, therefore they typically carry at least d4 of these specially enchanted acorns with them at all times. When they successfully hit another creature of up to 4HD, the creature must make a save versus spell or immediately fall into a deep sleep for d6 rounds.
Using their slings, which they are +2 to hit with, they will attempt to strike any target more powerful than they, and subsequently run their sleeping victims of all valuables. And clothes. Especially the clothes. These magically imbued acorns are only effective in the hands of the fey, if anyone else comes into possession of these and attempts to use them, they will simply turn to dust upon striking the target and impart no magical affect.