I read you could kill children in previous BG games. I remember clearly wiping out all of Beregost just to see if i could do it, and noticing children didn't care about fireballs. Was it changed?
Also, those particular gobelins are killable because they're part of the fight. That's all. And children in general aren't killable because that's a convention in most games, nothing more. It's just one of those points where you realize it's a game and therefore not a fully consistent universe.
For me it's a game design debate, not a political one. Since Larian didn't decide this 'no killing children' rule in games. Once you decided they'll be children playing in that camp, what could you do? They could pop off once the fight start, very immersion breaking. They could be invincible all the time except once the fight start, even worse. Or you can make them part of the fight and tell them to run away warn adults, wich lead to more story telling and an interesting gameplay choice, since they're quite fast^^. Mine usually find an empty camp so i just don't care^^.
What would be the point to directly confront the 'no killing children' rule in the tieffling camp? Nothing except letting players who just want to wipe out the grove to do it 'completely'. It's not worth breaking the rule.
And no, in Faerun, noone would think badly of you because you killed two young goblins rushing to their tribe to stop you from saving a druid. And eat you afterwards. You'd probably be criticized by the more zealous for letting them run away actually. Tiefflings however, if some knight told in a random tavern how he one day slaughtered them children alike, you would end up with a raging debate :p But the knight would be considered a criminal by the law anyway.
About fantasy and real life. I'm tired of the 'it's not supposed to be a reflection of the real world' thing. It's supposed to be a reflection of what? A universe where nothing is alike? Aren't the farmers growing food in exchange for money they need to buy tools and clothing in a feodal society? There are no empires, state-cities, pioneers and refugees? Are the wars fought because people don't agree about which color is the prettiest instead of land, economy, belief, political power? Are the rules for moral, demographic, art, history, logic, whatever, in the FR totally made up and making no sense at all? All those fantastical beings, gods themselves, aren't they moved by the same needs and fellings that move any beings in our real world? Last time i checked, players made characters driven by cupidity, lust, power, love, loyalty, knowledge, culture... and wanted to play in a world they could understand, predict, one where the setting is different but the rules are the same. It's not like if any author could invent different rules anyway. Racism, sexism and all those things some seemingly want to forget had always have been a strong part of the FR, notions used to ground this world. It define entire societies (looking at you, drows). And it was always depicted as a bad thing. Sure you can play a righteous zelot who slay anything that is different and think very good about himself. It's fine. But we all know than if the group stumble upon, let's say, a drow being burned by religious fellow for no other reason than she is a drow, the good choice is to free her. Even if she's evil, i guess deontology beat consequentialism in the FR. And it has all to do with the moral and political belief of the society in wich the game was made at the moment it was made.
It's interesting to see how it's precisely the issues we collectively still struggle to deal with that have the more weight in the moral outcome of our characters choices. For an exemple, you will hardly find any quest that confront the political system of the country/city you play in. If the king must be removed, it's not because he's a king, but because he's a bad king. If the council must be fought, it's not because it's not a democracy, but because its members are blind, corrupt, whatever.. That's because it's assumed we're all democrats, the debate is settled, so it's not very interesting to deal with, there is no tension. Since it's med fan, there is mostly feodal systems, but since it's fictional, you can find or make almost any system here and there, even anarchism :p Nobody cares as long as it's not totally unconceivable in a med fan world. But when it's about slavery, letting little monsters live or not, oppression, women in charge, military or diplomatic policy, religious confrontations, the place of strangers in a community... Now there's tension, now players will pick different options, probably quarrel with the DM about the outcome of their choices, and generally feel like those choices can build how their character see the world.
I wouldn't find role playing games interesting if my characters didn't have to position themselve about issues i actually care about. And i love playing an aristocratic, imperialist, expansionist, power hungry, and kinda racist human wizard. If the DM says it's evil when my character really think it isn't, fine, i did my job