It happened in 2015 with an image of the lifeless body of Alan Kurdi
, face down on a beach in Turkey, who drowned in the Mediterranean fleeing the war.
It happened last year when a photographer captured little Omran Daqneesh sitting in an ambulance
, his body bloodied and dusty after his home was bombed in Aleppo.
And it happened again last weekend, when a bomb hit a convoy of buses
carrying evacuees from besieged Syrian villages, killing 126 people.
Photographer and activist Abd Alkader Habak was there working and was briefly knocked out by the blast. When he came to, he began trying to help the wounded.
"The scene was horrible -- especially seeing children wailing and dying in front of you," Habak told CNN. "So I decided along with my colleagues that we'd put our cameras aside and start rescuing injured people."
The first child he checked on was dead.
He ran towards another. Someone shouted at him to stay away -- the child was already dead, they said.
But he wasn't. Habak could see the boy was barely breathing.
He picked him up and began to run towards safety. His camera was still on, recording the chaos.
"This child was firmly holding my hand and looking at me," he said.
An image taken by another photographer, Muhammad Alrageb, shows Habak dashing towards an ambulance, the child and his camera in his arms.
Algareb said he also helped some of the injured but then began taking photos.
"I wanted to film everything to make sure there was accountability," he said. Also, he added, "I feel proud that there was a young journalist there helping save lives."
Habak said he left the injured boy, who must have been only 6 or 7, at the ambulance. He doesn't know if the boy survived.
Then he ran back to scene of the bombing to help others. He came across another child on the ground. This one, too, was dead -- one of 68 children killed in the attack.
Overwhelmed, Habak collapsed.
An image, shot by another photographer, shows him on his knees sobbing near the boy's body.
"I was overcome with emotion," he told CNN. "What I and my colleagues witnessed is indescribable."