After 18 months of terror and grave devastation, Syrian children are plagued with trauma from witnessing the horrors of war firsthand, an international aid group says.

Save the Children released a report on Tuesday called "Untold Atrocities," a collection of accounts from Syrian refugee children.

"A massacre took place in my village. Around 25 people were killed -- I witnessed it with my own eyes," said Mohamad, 15, who has fled to Jordan with his family. "They used different ways to kill people -- electric shocks, throwing machinery and cement blocks on people's heads."

Hassan, 14, described the use of children as human shields, echoing reports from opposition activists that the Syrian regime had done so.

He said his cousin and uncle died when a rocket "caused a massacre."

"Almost every child we've spoken to has seen family members killed," Save the Children said.

Even those who survive attacks face dire circumstances.

"When we were being bombed, we had nothing. No food, no water, no toys -- nothing. There was no way to buy food -- the markets and shops were bombed out," Ala'a, 10, said. "My father went without food for days because there wasn't enough. I remember watching him tie his stomach with rope so he wouldn't feel so hungry."

Wael, 16, summarized the trauma this way:

"I have seen children slaughtered. I don't think I'll ever be OK again."

In other developments:

Diplomatic front: Obama pledges support, Qatar offers a new plan for Syria

U.S. President Barack Obama used his keynote speech at the U.N. General Assembly on Tuesday to pledge American support for those working for a "common good" for Syria -- and sanctions against those doing harm.

"In Syria, the future must not belong to a dictator who massacres his people," he said.

"If there is a cause that cries out for protest in the world today, it is a regime that tortures children and shoots rockets at apartment buildings. And we must remain engaged to assure that what began with citizens demanding their rights does not end in a cycle of sectarian violence."

French President Francois Hollande also had strong words on Syria, saying that areas "liberated" by opposition forces should be protected by the United Nations.

"There have been almost 30,000 deaths in the last 18 months -- how many more deaths will we wait for before we act? How can we allow the paralysis of the United Nations to continue?" he asked.

Hollande said France would recognize an opposition government once it is formed, and that the current regime had lost its right to represent the country on the international stage.

France has been at the forefront of international efforts to bring about a resolution in Syria.

In his address to the General Assembly, Qatar Prime Minister Sheikh Hamad bin Jassim Al Thani said the violence in Syria had reached "an unacceptable phase" and urged fellow Arab nations to intervene.

"We have used all available means to get Syria out of the cycle of killing, but that was in vain," he said.

In light of the U.N. Security Council's failure to act effectively, he said, "It is better for the Arab countries themselves to interfere out of their national, humanitarian, political and military duties and do what it necessary to stop the bloodshed in Syria ... in order to guarantee a peaceful transition of power in Syria."

His words come a day after he proposed a "Plan B" for solving the Syrian crisis, saying a nonviolent solution is still possible despite more than a year of relentless bloodshed.

In an interview with CNN's Christiane Amanpour on Monday, Al Thani said the plan would include havens -- which would require a no-fly zone -- and greater humanitarian aid.

"We wish and we believe that we can solve it peacefully," Al Thani said. But, he said, Syrian President Bashar al-Assad has only one solution: "killing his people to win the war."