Warning: This story contains graphic images of dead and injured children.
(CNN) -- They lay lifeless on the ground, babies, children and parents, some with foam coming from their mouth, families killed within minutes.
Body after body are splayed practically on top of each other on the floor of the room and up the concrete stairs, some of the children wrapped in blankets as if they had been asleep when the attack happened.
These shocking images, released on social media by anti-government activists, show the victims of an alleged chemical attack on innocent civilians hiding underground from conventional bombs in the besieged rebel-held Syrian town of Douma.
"Where is the world?" asks the man who steps over bodies as he films the gruesome scene. "That dog, Bashar al-Assad," he says. "Look at them, they were sleeping in their bathroom. These are the victims of a chemical attack."
The White Helmets rescue group said at least 43 people were killed and hundreds injured after the the deadly chemicals were released on Saturday night.
CNN could not independently confirm the veracity of the video footage or the accounts from the White Helmets.
The Syrian government and Russia, its key ally, have vehemently denied involvement and accused rebels in Douma of fabricating the chemical attack claims.
11 people from the Bakriya family and eight from the Al-Sheikh family were killed, according to a list of the dead compiled by the White Helmets obtained by CNN on Monday.
Many of the victims had been hiding in what appeared to be the basement of their homes to survive the shelling that has reduced this town, northeast of the capital Damascus, almost to rubble.
Mohamed Hassan Al-Masri, an anti-regime activist who told CNN he left Douma for Jarablus four days ago, saw the dead bodies of his friend Abu Hassan Al-Sheikh's children in the videos and pictures coming out of the town.
Al-Masri said one video shows 12-year-old Hassan and his sister Joudi, a one-year-old toddler in diapers, lying motionless on the floor next to a washing machine. Their sister, Heba, 10, wasn't in the videos, but Al-Masri said he was told by friends that she too had passed away.
Al-Masri said he didn't know what had happened to their father, Al-Sheikh, or his wife, whom he last saw 15 days ago.
Al-Sheikh, a building porter, was also supposed to leave with a convoy to evacuate civilians on Monday, Al-Masri said.
The family had moved hiding places four times since February, first escaping airstrikes in the neighboring town of Mesraba, then three times to three different places in Douma, mostly living in underground shelters and basements, according to Al-Masri.
"These three children were deprived of the basics of life," Al-Masri told CNN. "Joudi never got to taste fruit. They had no toys. They were a poor family. Bread was their main meal," he said.
Based on the videos and his previous experience with similar attacks, Al-Masri said he thought the children were hiding from airstrikes. He said the fact some of them died on the stairs suggests they might have smelled gas and tried to reach higher floors, "where the probability of being killed by chemicals would be less."
Activist groups, including the Douma Coordination Committee and the Ghouta Media Center, said barrel bombs filled with toxic gas were dropped from helicopters over the town Saturday, causing people to suffocate and choke.
Douma is the largest town in the farming and food production center of Eastern Ghouta.
A stronghold of forces fighting the Assad regime, it has been besieged for weeks. Tens of thousands of people have already fled other parts of the enclave after a two-month bombardment killed hundreds.
In a war where so much brutality has taken place that it seems no longer possible to shock, these graphic images, if authentic, show that people, especially children, no longer have anywhere to hide.