Welkin, the hero of the story, can potentially send her on a suicide mission to old an indefensible position, or act as bait for a tank, or run through a machine gun nest, knowing that he's sending a 12 year old girl to her death.
If you're going to send someone to their death, why NOT a 12 year old kid? 12 year olds are annoying as fuck, and require less than 67% of the production cost of an adult. It takes only 12 turns to produce a 12 year old, at least 18 to make an adult. That's at LEAST a 33% savings! It's simply easier and cheaper to turn out child soldiers, and they might even be better in many ways. So long as they can fire a gun, they also make smaller targets, and probably fit inside tanks better. If anything, I would intentionally design tanks to be crewed partially by child soldiers. You'd be able to put more armor on it because the crew would take up less space!
After all, does it really matter whether they die in battle, or die when they are dismembered and raped by your enemies when you lose because you weren't willing to do what it takes? A fighting chance is better than being the mop-up. This is why you see so many child soldiers employed in ethnic (and sectarian) conflicts: The losers will be massacred anyway, so they have a better chance of surviving by fighting.
