WASHINGTON (REUTERS) - In the video, a child's arm violently twitches, an image that left the US Senate Democratic leader struggling to comprehend a suspected chemical weapons attack in Syria that left an estimated 426 children dead.
"Pictures taken following the dropping of those horrible weapons, I will never get that out of my mind," Senator Harry Reid said on Monday after viewing a 13-minute video of Syrian victims.
"Little baby boys and girls dressed in little colourful play clothes. Boys and girls, some who looked like teenagers, retching in spasm," he said.
"These poisons kill the kids first. Their little bodies can't take this as well as older folks."
As the US political debate heats up over a possible military retaliation against Syria for the Aug 21 attack, President Barack Obama - as well as Mr Reid and other government officials backing limited strikes - point to the smallest victims in making their case.
For Mr Reid, images of children - part of a compilation of videos put together by the CIA that was made public over the weekend - were convincing evidence that the United States should respond to an attack by Syrian President Bashar al-Assad's forces.
"Without question his (Assad's) brutality demands a response," Mr Reid said.
Mr Obama, in a series of Monday television interviews that aired even as the Senate delayed action on a Syria resolution, cited child victims as one reason the US must ensure that Assad's forces do not use chemical weapons.
"Any parent who sees those videos of those children being gassed I think understands what a human tragedy it is," Mr Obama said in an interview on "CBS Evening News with Scott Pelley."
He also cited the youngest victims on Aug 31 when announcing his conclusion that military action was warranted and that he would seek congressional approval.
"What message will we send if a dictator can gas hundreds of children to death in plain sight and pay no price?" Mr Obama said.
A preliminary calculation offered by US intelligence agencies counted 426 child victims out of a total 1,429 deaths, an estimate made more vivid by real-time postings of images on YouTube and other social media.
The explosion of social media postings, including an early photo of a dying child, brought the attacks to public attention in a way that did not exist in 1988, when Iraqi President Saddam Hussein used mustard and nerve agents on the Kurdish town of Halabja during the war with Iran, killing up to 5,000 people, mostly civilians.
"Because of the prevalence of social media, it's impossible to hide - particularly something on the scale of this attack - these kinds of things anymore," said Mona Yacoubian, a Middle East expert at the Stimson Center.
Human rights groups say several factors explain the high toll of children. The attack occurred in the pre-dawn hours when families were sleeping and in populated neighbourhoods, including some where escape routes are blocked by pro-Assad forces.
The US estimate of nearly one-third of the deaths being children is also in line with the demographics of the country that show about 34 percent of Syria's population is age 14 or younger, according to the CIA's "World Factbook."
The Senate Intelligence Committee over the weekend posted on its website a compilation of mainly YouTube videos from pro-Syrian opposition sources that can be seen here: http: www.intelligence.senate.gov/syriavideo.html
"All of us are appalled at the gassing of children. But I am also appalled that many other children have died. A hundred thousand Syrians have been killed in this conflict so far. More than 2 million have been made into refugees," Republican Senator Susan Collins said last week.
Joe Stork, deputy director of Human Rights Watch's Middle East division, said the child deaths only underscore the horrific nature of chemical weapons.
"This is one of the reasons this is such a horrible weapon is because, unlike shelling, you simply can't protect yourself from it," he said.