The bomber also was a teenager, no more than 15 or 16 years old, judging by the picture of him released by the Islamic State, which asserted responsibility for the bombing, and the accounts of those who saw him at the match. The militants’ statement said the target was a gathering of members of the Shiite paramilitary group known as Hashd al-Shaabi, and the local government said two members of a militia were among the adults who died.

Yet that hardly explains the horror of an attack that inevitably would kill children.

The bomber “was a child, and he came to kill children,” said Mohammed al-Juhaishi, one of the sheiks from the area, who lost five relatives in the blast. “It was a children’s soccer game. Of course he knew he was going to kill children.”