It'll happen just like any other extermination of evil events that the Bible recounts. Now is the time for all, in case of minors, then it's up to their parents or guardians to make the right choice while there's still time.
Jehovah is a God of perfect justice; he hasn't changed. Whatever happens in armageddon, who ever is killed, will be plenty just as the executor of this can read the heart and see into circumstances that we cannot comprehend. Of this I'm sure, even if it implicates me for lack of faith.
So, you all trust in God and stop this silly obsessing over stuff one cannot control whatsoever.
DY