Yeah, all evidence we see in this game shows that even these goblin children, which seem more like goblin adolescents, are already murderous psychopaths.
Pretty much. Goblins have a deep sadistic streak. We see goblin kids in the camp who have tortured a person to death. For funsies.
They may be children but they aren't exactly innocent. Goblins function on an entirely different system of morality than the non-evil aligned races.
That said I still feel bad for having to kill them, but it very much is self defense at that point.