From The Waffen-SS in Allied Hands Volume One: Personal Accounts from Hitler's Elite Soldiers there is an excerprt of SS-Obergruppenfuhrur Wolff describing the rhetoric they used to indoctrinate recruits to justify their actions:

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Here's a Google Books preview link of the extract.

And here's an academic discussion on the gnostic aspects of Hitler's antisemitism citing his frequent use of the phrase.

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I've read it elsewhere too in the past, so there'll be more examples out there (Hitlers letters etc) but that's what I could hunt down quickly-ish at 2am with links.

Now, to be fair, Reinhold Niebuhr wrote a philosophical text at the very end of 1944 with the same title The Children of Light and the Children of Darkness but he did not originate the phrase and there seems to be earlier Nazi uses. It was in many ways an arguement for his rejection of his previous pacifism in the 30s. Primarily it argued that naive and hopeful democracies (Children of Light) must be able to confront violent and undemocratic states (Children of Darkness) and that to do so, may have to borrow some of their tactics while not becoming blinded by the same "malice" they have. It is, from what I remember, basically philopsocial and theologian argument for states carrying out foreign intervention, with some good points about the need to confront fascists for example, while also treading a pretty thin line (generously) about moral intention as a differentiator between 'democratic liberal states' who use violence, force, and potentially 'immoral' tactics and the 'undemocratic illiberal' ones that do the same. Naturally its beloved by modern Liberal politicians, mostly for the worst reasons.

So while you could argue Netanyahu and other Israeli state and media figures using this line had no idea Hitler frequently used it to justify genocide, and instead only known it from Niebuhr, I think given the context that its being used in - the advocating of what those using it absolutely know aapnd understand is genocide - that's pretty unlikely. And even if that were the case, and they were unaware of the Nazi connection, they're still using a moral arguement based in the idea of 'the right people' being able to use the tactics of 'the wrong people' to justify genocide. In exactly the same way the Nazis did.

I would argue there's a lot of true believers, they were already making money in Ukraine sending Wunderwaffe. There was a story of a large split at the state department pretty early on too where half were on board and the other half were being pragmatists stating that it'd ruin the US's position with third world nations.