The vast majority of people in this World see the killing of other human beings as something that covers a moral range, with something like self-defense when in direct danger for one’s life being at the more acceptable end of the scale and the killing of the young children at the more unacceptable end of the scale.
This moral scale within murder also applies to the murderers themselves, which is why - as I pointed out earlier - in murder statistics and deaths in wars, children form a far smaller proportion of the deaths in comparison to the total of children, than people of other ages for in proportion to the total of people of those ages.
So even if you yourself haven’t a heightened sense of revulsion for some murderes versus others (which, by the way, is not normal), even people who kill other people generally find the killing of children harder or even unnacceptable.
In practice child murder is pretty well correlated with the highest levels of sociopathy and psychopathy, so a military which practices high levels of child murder has higher levels of psychopaths and sociopaths in their midst and leadership, and they have freer reign to act in psychopathic and sociopathic ways with no punishment - there are always some psychopaths and sociopaths in the military, but there being so many that child-murder is a generalized practice including specific targetting children - for example snipping children or bombing playgrounds - is incredibly rare.
We saw this with the SS and the Nazis, and we see this with the IDF and the Zionists.