I don't see the problem.
All the game set is based on a land where there are continuous wars, raids, I find quite realistic the fact that Larian decide not to make a childless or a "child safety first" background, also because in the writing they highlighted how the wars and conflicts affect the children (Will, the thiefling training the kids, the druid that opposes Karath, all of them make clear how they don't like how the little ones are involved), Larian show us how the situation affects them. We have the silent red thiefling boy (why does he doesn't speak? ), the kid who has lost his eye, the ones that have become thieves.
Furthermore Larian gives ways to solve everything without a massacre thus allows to save the children (well it depends on your luck and/or will to reload), I was able to save Arabelle, to avoid the massacre of thieflings.
Always on Larian trying to show how conflict and environment had an impact on kids we have the four ones in the Goblin Camp, two of them hit the corpse of an adventurer and they don't accept to be repimanded because that man had killed their parents, the ones throwing stones at Halsin/bear, are following the example of the grwon ups and thus end being mauled because in a place where they shouldn't be.
Moreover if i remember well the only kids that can not be saved are only the ones stoning the captured Druid, Arabella can be saved, the kids hitting the corpse are not there after the leaders are killed.
Also I think that using kids in the opening chapter is another cliché used by Larian, in OSD2 there are four kids, and again to see them is useful to understand the influence and impact of what is happening (in OSD 2 the magic people being imprisoned ).
