There is a massive difference between an oil rig exploding and the party sending a kid into a dungeon with nothing but a torch.
To be clear, what is being talked about here is the party knowingly sending a kid into a dungeon ahead of the party with nothing but a torch. The kid has no weapons, no armour, no training and no chance of survival in the event of actually meeting an unfriendly group of monsters (also likely no chance of survival in the event of a trap but if the kid is lucky/smart enough, they may spot the trap so at least this isn't guaranteed death). And clearly, the party is alert to the possibility of trouble otherwise they wouldn't have hired the kid in the first place.
This isn't simply a case of something going wrong leading to the unfortunate death of the kid. In the case of real life dangerous work, believe it or not, there are precautions taken to try to minimize the amount of danger. Granted, you can't eliminate the danger entirely and some of this is predicated on the company/people actually following the law/rules/regulations etc but the point is that companies can't simply send people recklessly into dangerous situations without consequences (whether those consequences are severe enough is way outside the scope of this discussion and probably puts this too close to beekeepers so I'm not going there).
Going back to the original situation of the kid being sent into the dungeon in front of the party - saying that the party isn't responsible for the death of the kid is, in my opinion, equivalent to arguing that gravity is the killer and not the person who pushed the deceased off a tall building. It that happened in my group, I would immediately make the party evil (assuming they all agreed to go along with the plan) and they would suffer the consequences of being an evil party (obv, I would make them aware that what they were doing would result in them being of evil alignment). To be clear, I would also make the party evil if they armed the kid with a sword and armor. In fact, the only situation where I can imagine not making the party evil is if they made the kid a part of the party - ie he travels with the party and not 10" in front of the party.
The last point I wanted to make about alignment is that Good or Evil aren't absolute concepts but relative concepts. Discussion of Good or Evil in itself is a massive topic which philosophers have discussed/argued about for years and trying to get into that in any depth in an RPG is more than I have any interest in for the purpose of a game. When I run an RPG, alignment is determined based on what I consider is Good or Evil which in turn is based, to an extent, on what society currently considers as Good or Evil (or Moral vs Immoral - or Right vs Wrong - or well, take your pick as to terminology as they are all subtly different - again, way too deep a subject to explore for the purpose of playing an RPG).
My point is that there are many things which have happened in the past which were considered moral at the time but are no longer considered moral now (arguably, you don't even need to go into the past for this as there are many things happening today which some people see as being moral and good while others see as being immoral and evil). Again - way too deep a discussion for the purpose of playing an RPG. However, as the DM, if the player's argument for something not being considered Evil is simply that it was considered acceptable by people at some point in the past, your argument isn't going to get very far with me as I have no interest in playing that game.