It is wrong to kill or perform any violence or harm against children in any war context.
I'm not saying death and murder is okay. I'm saying coutries do what they have to do by means the have (or they think they have).
You haven't thought this through.
It is the nature of life itself to "kill and perform violence", children and otherwise. "The strong do what they can, and the weak suffer what they must".
Death is, as of now, life's only mechanism for iteration in its process of endless prototyping.
Every marvel that humankind has produced has its roots in extreme violence. From the creation of Ancient Greece to the creation of the United States, children had to die horrible deaths so that these things could come to be.
Anyone can make arbitrary claims about what's right and what's wrong. The only way to prove such a claim is through victory, and all victory is violence against the loser.
I am disgusted that this is still proferred as a valid moral philosophical principle. No. A thousand times no.
The answer is A SYSTEM.
The answer to bully predator logic is human society and systematic thought. This provides the capability to resist such base immorality as you and historical predators have proposed.
There's no way out of violence, your system needs to be founded on it.
And I wouldn't say that the what previous poster described is akin to witch trials. It's rather akin to painting the bullseye labelled "right" after taking the shot and hitting something other than your foot. And that was what all human cultures were doing since the beginning of time. Recent western trend to paint the bullseye labelled "wrong" at their hit is novel but equally disingenious.
Can you explain what makes it invalid besides the fact that you and me don't like it?
There are no "valid" or "invalid" moral principles, there is no objectively correct morality, nor does the idea even make sense. Morals are historically contingent social phenomena. Over different times and even over different cultures today, they vary dramatically. Everyone has them, and they all think they are right. That quickly reduces all discussion in cases like this to ornate versions of "you're wrong" and "no, YOU'RE wrong."