why is Hamas, who breaks every rule of war and does things that even ISIS didn't do, given a free pass on their war crimes?
PR. Hamas deliberately organizes things so that children die when Israel attacks. Since the world learned, from Judaism via Christianity, that children shouldn't be killed, it takes issue with those who're actively killing the children. The aspect of those children being put in place to be killed by Hamas has no bearing in this, because Israel is in the unenviable position of being able to opt not to shoot / explode / starve the children Judaism taught the world it's wrong to shoot / bomb / starve.
Yes, this is a Catch-22. Either Israel fully avoids shooting, bombing, and starving those children, giving Hamas a strong strategic advantage it'd need to overcome in some other way (that doesn't involve shooting, bombing and starving children), or Israel embraces the shooting, bombing and starvation of children to uproot Hamas, thus becoming monsters before the very world their great-great-great-...-great-grand-forefathers taught "do NOT kill children".
I feel like I understand the 1930's so much better today than I did a year ago.
There are echoes of that. Until the 1930s Christian antisemites regularly accused Jewish people, falsely, of murdering children, which all by itself had led to several Pogroms. Hamas is obviously taping on that. The problem is, nowadays there are photos of the murdered children, whereas back then there were, quite literally, no murdered children at all.
Hence, while the analogy is there, and parallels can be traced, the core difference is that in the 1930s the accusations were false, while in 2020s they aren't. Yes, again, this is deliberately being engineered by Hamas. But there's no sidestepping the fact the world is intensely horrified by the photos of dead children. And the longer this continues, the worse Israel's international image will become.
So, PR-wise, the best approach would be to, you know, stop killing the children. Not reducing the rate of children killed per month of whatever, that doesn't work in a world where the video of one children who dies will be repeatedly shown all around over and over and over. A total, full stop. That's what it'd take, at the bare minimum.
That's basically it. Not a sudden global pandemic of antisemitism, which isn't really happening, no. Dead children. No more, no less.