system
Given the following post, respond as if you're commenting on Reddit:
human
CMV: having child NPCs in open world video games shouldn't be a problem.

The vast majority of open world video games that feature human NPCs (GTA and the Assassin's Creed games come to mind) all of the NPCs are adults. I've not seen any developers officially respond to the issue but most fan theories tend to be something like it would be too taboo to allow the player to kill children, which would explain why the few games that do feature children (such as Skyrim) usually make them invincible, which I think is more comical and unrealistic than not having any. But by what standard is it ok to allow the player to gun down countless unarmed adults but children being a step too far? There's also the suggestion that including killable children could lead to negative media attention. I simply don't think this would happen, in the Sims games its possible to trap children in a doorless room and let them starve, which is arguably worse than killing them violently, and yet EA never gets any backlash for that. 

This is an issue that I've only seen discussed lightly, so it would be interesting to hear if there is anything I haven't considered.
gpt
The reason for why killing children isn't in most games is because the ESRB will almost certainly give games an AO rating for showing a player character killing children (this is why, in Bioshock, harvesting the Little Sisters is done with a fade to black), and AO games are basically unsellable because physical retailers have a blanket policy against it. That isn't a fan theory or something developers would respond to, it's just like... a fact of the industry.

Anyway, violent games that push the edge of good taste can still attract negative media attention; see the game Hatred for an example of a game intentionally leaning into this. What little there is to be gained from allowing players the freedom to kill children would almost certainly be lost because, well, you made the game that's most notable for being the game that lets you kill children. The Sims example just seems bizarre to me; it seems extremely obvious that people react more viscerally to violent murder than simulationist neglect; you may as well argue that being able to call down a tornado in Cities: Skylines means it should get a higher rating than performing glory kills in Doom, since the former kills way more people.