Criticism of Children at War

P.W. Singer's work "Children at War" is a great source with flaws. The works most glaring flaws is that it claims before WW2, civilians (especially children) were "never targeted by any combatants before the pre-WW2 era". This claim is almost comically inflated if the subject matter wasn't so tragic. In fact countless examples of armies deliberately targeting combatants before WW2 is so common, that I can't even put a small percentage of examples on this post. However, I will post some cases in my post of civilian massacres before WW2.
1. In the Japanese invasion of Korea in the 17th century, Japanese army has been known to sack towns and massacre every living thing they encounter. In the words of one commander "we beheading everybody of all ages and genders. Even cats and dogs were beheaded".
2. In the Peloponnesian War, a couple of Thraican mercenaries stormed a boys school and killed every single child in the school.
3. When Fredrick Barbarossa besieged the city state of Crema, he even catapulted childern aganist the walls.
4. The Mongols are notorious for slaughtering entire cities, even killing the cats and dogs. One source when mentioned the massacre of the Tanguts for refusing to give the Mongols horses, mentioned that "we might never get records from the Tanguts, since nobody survived to record the events"
Although the work has it's flaws, its greatest strength is that it gives great information on many non-state groups around the world. It would have been better if Singer give his Achilles's heel some armor.