The answer the Israeli government would rarely admit (I was going to say never, but then I remember Israel's president Herzog saying there are no civilians in Gaza), but IOF members have said repeatedly, is that they see those children as future terrorists.

Now the ordinary liberal might be inclined to believe the IOF would kill children but feel guilty about it, doing it as something they see as a necessity, but in reality you have literal tweets from Israelis looking at crying children and swearing at them and promising to kill them; they don't see a child in Palestinian children (or even any non-Jewish Middle Eastern children for that matter), they see them as adults; Fox news referring to black children as young men is something they do intentionally to get people used to the idea of seeing black children as adults, Israelis just naturally see non-Jewish Middle Eastern children as adults.