Let's make a Space Opera

Something else that would be shocking is an enemy with no qualms about killing Child Soldiers. An alien or a robot wouldn't see a child, only a soldier, and thus a threat.

A very good argument can be made for why a modern military couldn't have qualms about killing child soldiers. Yes, they're children, but they're also soldiers, in the strictest sense of being armed combatants, usually in the employ of an opposing government or armed force. Sure, killing them is morally abhorrent, but the soldiers on your side are more important. I wouldn't let my soldiers die just because the enemy is using children. That would be letting them win. The only way to stop them is to stop them, so they can never do it again. If you can capture the children, that's good, but you can't be a martyr because you can't handle killing them even as they shoot your ass to bits.

In a futuristic setting disarming them should be somewhat easier, using some sort of fancy technology.

And yet mecha shows teach us that, children or not, they can have effective grasps of how to use advanced warfare technology, especially stuff that's tailored to their use to minimize the fact that, well, they're children, such as a mentally-piloted giant mech. How do you disarm that, short of obliterating it? Child soldiers doesn't necessarily imply they're using nothing but small arms, which makes them an exponentially more impressive threat.

Then we still got problem. EM Ps are a good way to disarm mech-wielding children. Directed plasma or electrically-charged projectiles work as well.

This is true, but EMP strong enough to damage the craft and disable it is likely strong enough to kill the pilot, too, if the craft is realistically EMP-hardened...

Well, that's where options start running thin.

Exactly. Child soldiers are, in the end, just that, soldiers. If the enemy sends inexperienced and inept militia at you, you still shred them. Child soldiers are exactly that, but younger, so as to invoke such a parental mentality among the enemy. If one gives in, the enemy wins. I would never, as a professional soldier, want to encounter a child soldier on the battlefield, but the immediate mentality should always be "shoot first and ask questions second." One's own soldiers' lives takes priority among enemy soldiers' lives. If one may possibly be able to capture child soldiers alive, great; I'm not advocating "take no prisoners." But going in with a "they're kids, we can't kill them" will only get one slaughtered.

And that's exactly who they are facing in that story. An enemy who cares not about collateral damage (sometimes even outright deliberately attacking civilians and civilian areas) or who they are facing. This is in stark contrast to the Terrans, Feyline and Preyarans who all admit collateral damage to civilians can and will happen but never deliberately cause it. Such is the way of the Vyron, anything to accomplish their goal set out by Mikhail Voronov and Mistress Bellah is a valid tactic including outright terror tactics up to and including practically grinding an entire species to nothing.

I heard you list several species byt I'm not too familiar with 'em. C Ould you give me a brief run-down?

Long ago, humans left a dying Earth for what is now known as “The Cluster”. There seven planets – each orbiting a different star – were found and colonized. Other stars did and still do exist within the Cluster, but either they had no habitable planets or were too far away to be worth the effort.

But that's ancient history. Now all seven planets have been colonized and are nations in their own right. They are close enough to each other that travel between them is not uncommon, but have no interest in unifying and all efforts of one to conquer another have thus far failed. So they are forced to tolerate each other.An uneasy peace exists between the worlds of the Cluster, punctuated by the occasional naval skirmish or hired mercenaries. But at any moment, things could erupt once again.

Meanwhile, there are rumors of an eighth planet somewhere out there. It's said to have everything from super advanced and potentially hostile or benevolent aliens to a bountiful natural paradise fresh for colonization., but no-one really knows for sure.

That's the foundation I've got so far. I'll detail the seven worlds themselves once I'm sure the foundation itself isn't flawed in some way.