There were 8 dead bodies ranging in age from 7 to 10 on the ground. The body had been crushed or cut into several pieces.
It even made professionals who had witnessed countless dead and slain thousands of monsters feel like vomiting. They had never seen someone so cruel.
In war or a life-threatening battle, they had seen many dead bodies but they were all adults. In wars too, there is a minimum level of respect for the people.
No one would deliberately kill a small child. Given the option, many would avoid it even if they were on the enemy side.
But what they were seeing was the cruelty of the enemy that they had yet to encounter. They don't know who their enemy is but they did know that he/she was sick in his head.
Judging by the scene, they could tell that the murderer had obviously targeted those kids specifically. If not, there would also be some dead bodies of adults.