how did you encounter Mol before doing the harpies i.e, what steps in what order?
(1) I'd helped the kid who stole the locket.
(2) I got pickpocketed.
(3) As a Dwarf, I was able to chase the pickpocket into the hideout.
Because of step 1, Mol was willing to give me back my stolen inventory, but there wasn't any further acknowledgement after I helped the other two kids. Which isn't a big deal, but it leaves the remaining open quest.