So, for me, this has two different aspects.
The first is this: kids die. They die in war, they die from neglect and abuse, they die from exploitation and slavery, they die from terrorrism, they die in genocide. They die in the Mediterranean trying to cross to Europe as refugees - and after the EU frobade assisting them, they died in Aleppo from indescriminate bombing, they died in camps on the American border after being separated from their parents, they died by the Khmer Rouge, and in German concentration camps. They die as collateral damage (like the hundreds of thousands killed by the American atomic bombs on Hiroshima and Nagasaki), they die deliberately and specifically (like in the facilities built by the Germans in WW2 to investigate specifically the mass murder of children), and they die because we don't care (like the girls who die in sweatshop fires in Pakistan, so that Western stores could sell cheap textile). The human race is aweful. That is the reality of our species, and there is no point denying it. In a way it is almost criminal to do so. (the above is just stating facts, not an invitation to discuss politics)
Which brings me to my second point: The framing of this infanticide. I think we can all agree that killing children is an evil thing to do. Even if you are one of those, hmmm... I wanna say trolls, who advocated for more ways to kill children. And so killing them in the game should be framed as evil. The killing of Arabella was well done because Kagha was portrayed as a corrupt and evil individual (which is why her repentence seems a bit too easy, for my taste), But Halsin's slaughter of the goblin kids is presented in a very different way. Yes, goblins are evil (although Larian stated several times that they were stepping away from portraying whole races as one alignment) , but these are still children. And Halsin should not be presented as a kindly uncle after this murder. So yes, if he is to stay a positive character (or at least a non-negative one), we should be given at the very least an option to restrain him from infanticide. The same goes for any non evil character who kills children.