Animals don't have, if you notice, evil laws. They simply abide by the laws that nature has provided them. We humans are the only ones who develop evil laws. Even wolves, who attack and eat other animals, are not being evil. They're simply fighting to survive. It is nothing personal. They aren't attacking deer or whatever out of spite or envy. They aren't enslaving people so they can build grand monuments to honor themselves. They kill out of necessity.
This is why I said that I don't actually have an issue with killing the goblin kids, but I do with killing the tiefling kids. Killing the goblin kids is done out of necessity in order to save Halsin. They are evil, people-eating monsters who are about to eat poor Brian who is cooking on a spit. On the other hand, killing the tiefling children is done as an act of pure bloodlust and butchery. The kids aren't evil. They might be mischievous, but not evil.
So, yes. I have a problem playing an evil character killing a bunch of not-evil tiefling kids. Can I just not play the evil path? Absolutely. I certainly can. But, that's not the point. The point is that Larian is the DM. If they're comfortable with allowing players to kill the tiefling children, then fine. Let players be truly evil and go about butchering children. They're just pixels anyway. Right?
Do I like killing the goblin kids? No, but I can at least understand that if I don't kill them, they're going to summon more goblins to try to kill me. I can also rest in the knowledge that goblins are evil - or at least they used to be based on previous canon, and at the very least this tribe of goblins is butchering and eating people, so these goblin kids are at least evil.
The tieflings, on the other hand, I can understand Larian not wanting to let you kill them. They are NOT butchering people and eating them. They are NOT trying to kill you - except in situations where they get adults to try to kill you, in which case, I agree that in that case Larian needs to provide some alternatives to you getting attacked by the entire tiefling camp and there's nothing you can do about it but reload or kill them all.
Anyway, bottom line is, and my point is, that when you don't draw a line, you start to slide to a very dangerous place bordering on the criminal. Aside from employees at Larian maybe feeling guilty about things they are forced to do because some people might want to be a bit over the line, I have seen how not drawing the line often ends up. Cross the line too many times, and you fall off the edge of a cliff.
First of all, natural law is not understood perfectly. Physics is not understood perfectly. Our laws are far from perfect, and we have yet to create a perfect set of laws and a perfect society, so human understanding and implemetation of law is flawed.
Second, you're just plain wrong about animals. There are animals that kill for pleasure. An entire species of animal we commonly refer to as the house cat kills just for fun. Other examples exist in nature, just not on a large scale, but then you really can't say that humans kill for pleasure on a large scale either. The Tsavo lions were belived to have been two such animals, but there are countless examples out there, this is why we kill any animal that kills a human.
Again, it's hypocritical to make a judgement saying that it's okay to kill one set of children, but not another. Once any type of children are killed, that theoretical line you worry so much about crossing has already been crossed. That being said, it doesn't require a video game to get humans to kill human babies. In war, as well as times of peace, babies are always victims. Either directly murdered, or abandoned to die. This a something that happens in real life all over the world, every single day. It may be sanctioned by a government, or encouraged by a local warlord, or just a mother who discards her baby in a dumpster. It may also be a stray bullet that hits a six year old in the streets of Chicago.
Anyway, bottom line is that censorship starts with people who feel a need to draw a line. You want to fix the world, start in the world. No matter whether you succeed in getting a piece of fiction censored to fit with your moral beliefs of not, it will have changed nothing of consequence. Even in the game it will fail to achieve the goal you seek, because children will still be dying on the streets, just not the children you seem to care about. The message will be that you should only kill the ugly children who misbehave, or perhaps it will be interpreted as the uneducated children, or just poor children. Discrimination is one of our most obvious flaws, yet poeple keep doing it.