1) You don't actually have to kill the baby to forcibly shut it up. You should be able to gag it (not healthy exactly but it'll do the job) and/or induce unconsciousness without doing too much damage. For reference: "The use of choking to induce unconsciousness is a temporary incapacitating technique of short duration whose proper execution is quite harmless." Admittedly, this is not going to be easy if you're trying it on a baby, but worst case scenario you kill it (which you were probably going to do anyway), and best case scenario it's unconscious and you all survive. You are assuming that I have enough time to actually do something before the soldiers identify the source of the sound (we're actually probably looking at hearing), though, and you may even be assuming that if the soldiers cannot identify the source of the sound that they will not check every building (this is false, by the way). So my guess is I have at least 8-10 seconds, perhaps even 15, which is more than enough time.
2) Define "certain to die soon". Further, are there sharks? How far out at sea are we? I can swim; bring it on.
3) Flip the switch and go save his inattentive ass. It's a lot easier to save one person than five. For this version of it you can argue that it's not possible since I'm not on location, but it doesn't work for at least the second one and possibly the third one. Still, if you can flip the switch as the train hits it, then we can either get a stuck train or a derailed train, in which case no one is in the path anymore. Yes, I'm aware that would be tough.
3.1) I'm not understanding how this works, but my theory is him getting hit by the train is supposed to alert the other five to it and/or slow the train down enough for them to get away (note: extremely unlikely, as he's made of flesh and bone). In case it's the first, my pants should do the job as well, unless we're looking for a crunch noise, in which case, I'm not sure what I have in my pockets that day.
3.2) Same as above, I'm not understanding how this is a valid solution to the problem.
3.3) For the record, if these people are standing on the tracks, then I'm not sure I want to save them in the first place. If, however, we've got some kind of thing going on where track is unfinished and the train in question is going to be going off of the track, then we may have an actual issue at hand.
The first and the second one aren't bad, exactly...in terms of decisions, at least. The third one seems unnecessarily complicated any way you put it.
At least you can determine from my responses that I am 1) too moral and 2) too logical to accept that the options you've given me are the limit of the options that I have.
This reminds me somewhat of the theoretical situation where there's a fire in a building and you can save x amount of people on one floor or you can save y amount of people on another floor. It doesn't work like this. It really doesn't. Saving a given person is going to take you a amount of time, getting back in to save another is going to take you b amount of time (we're assuming that you can't save them all at once, i.e. they're unconscious or something and simple reason/helping them over a single obstacle won't cut it), and unless the fire started on one of the higher floors and you're trying to get people out from the lower floors (read: kind of stupid, as it tends to go upwards, but will eventually burn the building down, so the floor the fire's on should be prioritized first), you're simply not going to have enough time to get perhaps two people out, most likely one, before you just can't fucking get back in there anymore. This is why we have firefighters, people. (Also Spider-Man. But let's not go there, okay?)
Also, unless this is a chemical fire that's going to cause an explosion in a very short amount of time, in which case you're going to have a helluva time even getting one person out, where the hell are the fire extinguishers? I thought we had to have them by law by this point. Maybe that's just this area? I guess forest fires help for something.
Yes, I know I added an example you didn't even include and might not agree with, without fleshing it out to boot. But it seemed to be somewhat relevant.