Not sure if we are still in the era of " Games propagate mass murder " journalism but just in case I guess Larian is better of not allowing murdering kids. I would straight up make it easily moddable but not make it possible by default.
It might be out of date, but I am pretty sure some regions would outright ban the game - I think that's why New Vegas didn't allow killing children. I do question why we can kill goblin kids though - they are definitely sentient enough. Perhaps, that's Larians way of giving players Fallout1 level of freedom through monstrous children?
Fallout 3 had the same issue. The kids in Megaton had to be made unkillable.
I believe Germany for 1 would ban the game outright if it allowed players to kill kids. Some other countries as well. Larian is NOT going to change that in BG3 or they would be cut off from select markets.