BEIRUT, Lebanon — Omran Daqneesh, a small Syrian boy from the embattled rebel-held section of Aleppo, somehow snapped to attention millions of people around the world, who watched and shared the arresting video of him as he wiped dried blood and thick soot from his face.

The widespread interest in 5-year-old Omran surprised the doctors who treated him, the photographer who shot the video and many Syrians who wondered whether the world had only just discovered how children have suffered every day in a war that has raged for more than five years.

On Saturday, Omran’s 10-year-old brother, Ali, died of wounds he suffered during the same attack, medical workers said. Ali’s death, which did not draw the same instant social media outpouring as Omran’s suffering, only underscored how many Syrian children are dying under the radar of the wider world.