The general rule of thumb is that computer games never offer all options, like only a real tabletop session can.
So theres no option to kill all the Tiefling kids. I would assume that Larian simply hasnt come up with an appropiate reaction to such an act, thus they dont allow it.
Also I guess one may argue that these kids are especially resourceful with thievery, and thus would be able to escape any such murder attempt.
Is there anyone who doesnt ?
