Witnesses at Sandy Hook Elementary School reported horrific scenes as a shooter took 27 lives today -- the shattering sounds of gunshots, children locked in the bathrooms and parents crying outside in the parking lot.
Experts say that the young children who saw events first-hand can have lasting psychological scars, but those whose home lives are stable and supportive will have fewer long-term scars.
"It was horrific," said Kaitlin Roig, a 29-year-old teacher, who was in a morning meeting when the gunman entered the school.
"Suddenly, I heard rapid fire, like an assault weapon," the first grade teacher told ABC. She rounded up her 14 students and locked them and herself in the bathroom. "I helped kids climb on the toilet dispenser [so they could all fit in].
"I thought we were going to die."
Children in such a situation "are terrified, and they don't have the cognitive or emotional capacities to make sense of this," said Dr. Nadine Kaslow, professor and vice chair of the department of psychiatry at Emory School of Medicine.
"Not that any of us can make any sense of this," said Kaslow. "It's truly inconceivable."
At least 27 people, mostly children under the age of 10, were shot and killed at the K-to-4 school this morning, federal and state sources tell ABC News.
The massacre drew SWAT teams to the school and the town of Newtown locked down all its schools, authorities said today.
According to federal sources, the gunman was identified as Adam Lanza, 20. His mother, who worked at the elementary school, was one of the victims.
One mother named Christine who has a child at Sandy Hook told ABC about the chaos that ensued when she arrived at the school this morning.
"When I got there, there were just parents running into the firehouse because they were directing us there. That's where children had been evacuating to, and we went in and people were just grabbing their children and hugging and crying. There were lots of children crying."
She said another parent who had been at the school at the time was "pretty broken up." Many parents didn't know where their children were.
In 1996 in Dunblane, Scotland, 15 children and a teacher were killed in a similar massacre.
Parents and caregivers play the most important role in a child's recovery from a traumatic event, according to Dr. Gene Beresin, director of training in child and adolescent psychiatry at Massachusetts General Hospital.
"Children need to know that they are safe," he said. "Are people taking care of me? How is this going to affect my life? They need to be reassured."
"Thinking about kids in all disasters, you think about the airlines -- when the oxygen mask drops, you put your mask on first and then help the child next," said Beresin.
"Parents need to take care of themselves first. [The children] need to know you are calm and in control," he said.
Adults and community support is critical, according to Beresin.