Where are you in the game? The first time that happened to me was in the slaver quest under the copper coronet- when you go up the stairs into the slaver ship/stronghold, the first battle you have, if you let one of the slaver gaurds get away and up the stairs, they will kill the two children that are in the rooms on either side of the hallway before you get to the first yuan-ti. I could not figure out what the heck minsc,jaheira and aerie were complaining about, til i read a walk thru and figured out what the 2 bodies in the big rooms that look like they have a net for a floor were - the children i was supposed to free! reload...
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When given a choice, take both.