During WWII, the entire Allied leadership was willing to kill millions of Axis children if that's what it took to win the war and force the enemy to surrender unconditionally. There was at least some genocidal intent. Population centers were intentionally bombed to wipe out civilian factory workers. We can argue about whether that was right or wrong but the reality is that it's probably inevitable once armed conflicts involving nation states escalate to an existential level.

“Before we’re through with them, the Japanese language will be spoken only in hell.”

-- Admiral William F. "Bull" Halsey Jr., 1941