NEWTOWN, Conn. (AP) — A few nights after the massacre at Sandy Hook Elementary School, David Posey heard a strange noise in his house and went upstairs to check on his son. The little boy, who had just seen his teacher and a first-grade classmate gunned down, was pounding on the floor.

"I know where the bad guy is," the child told his father, indicating down below, in hell. "I'm beating him up."

Hundreds of children at the school that day survived the shooting, but the horrors have been especially difficult to overcome for some of the 6- and 7-year-olds who witnessed the bloodbath. Among the survivors are a dozen first-graders from the two classrooms where the gunman opened fire with a semi-automatic rifle.

Nightmares are persistent, and any reminder of the attack — a fire alarm, a clap of thunder, even the sound of an intercom — can stir feelings of panic. At the building in a neighboring town where the survivors recently began a new school year, signs ask people to close doors softly and not to drag objects across the floor.

Their parents, grateful their children are even alive, have struggled out of public view, another set of families left reeling from the attack. For all the hugs and assurances they are safe, the parents can no longer tell their children there are no such things as monsters.

"The worst part is the helplessness," said Hugo Rojas, whose son also witnessed the shooting. "You want to take that pain away. You want to be able to take those nightmares away, but you can't."

The gunman, Adam Lanza, who killed 20 children and six educators at the school, shot his way into the building the morning of Dec. 14.

As the sound of gunfire and shells hitting the floor rang out from the hallway, the children in Victoria Soto's class were moved to the back of their room. They were sitting on the floor when Lanza burst through the door. No one spoke, not even Lanza. The gunman pointed his gun at the face of Posey's son, just inches away. But he didn't shoot him.

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"He said he kind of just stared down the kids," Posey said. "My personal belief is that at that particular time he hadn't crossed the threshold of shooting a child."

Lanza shot the teacher. And a girl. As Lanza reloaded his gun, children including Posey's and Rojas' sons ran past blood, shattered glass and the body of their principal, lying on the hallway floor. After firing off 154 rifle shots within five minutes, Lanza killed himself with a handgun as police arrived. He also killed his mother that morning before driving to the school.

Posey and Rojas described in interviews how any reminder of the attack would traumatize their sons. To protect their privacy, they asked that the boys' names not be published. Most of the families of the surviving witnesses have tried to shield their children's identities and struggles and have declined to speak publicly.

Two months after the shooting, Posey and his family were in the grocery store when an announcement came over the intercom. His son insisted they leave immediately. Posey was baffled, but his son later explained the intercom was on when Lanza began his rampage inside Sandy Hook.

"'When the intercom goes off, that's when something bad is about to happen,'" he recalled his son telling him.

Posey also noticed changes in behavior. His once agreeable boy began to rebel, refusing to brush his teeth. He started wearing his Batman and Iron Man costumes again.

"It's his ability to be a superhero and in control," Posey said. "People don't hurt Batman."

Rojas said his son, who is in therapy, has had to cope with vivid nightmares. His son does not talk much about the shooting, but he sometimes asks why. The family tries to be honest, telling him they don't know why. He also asks about his friends who were killed.

"We talk about heaven," Rojas said. "He knows they're there."

The families of the 12 surviving children who witnessed the shootings each received $20,000 from the largest Newtown charity fund. The families of the 26 people who were killed each received $281,000.

In a letter to the foundation in charge of distributing the donations, Newtown First Selectman Patricia Llodra said $20,000 is not nearly adequate for the families of the survivors, who are likely to need counseling for years.

"Twenty thousand dollars will be insufficient to address the wide range of mental health needs for these youngsters and their siblings and parents for years into the future," Llodra wrote in the Aug. 7 letter urging the foundation to set aside money for the families' future needs. "Please be aware also that many of these families suffered significant loss of income and loss of opportunity during the months immediately after December 14."

On the day of the massacre, Posey's children, including two at Sandy Hook, were attending their final day of school in Newtown before moving to Colorado a day later. In Colorado, Posey and his wife have joined survivors of the 1999 Columbine High School shooting to form a foundation to help schools prepare emergency plans and help survivors of tragedies to recover. He is also working with parents of Newtown victims on an effort to improve school safety.

With time, Posey said, his son has shown signs of recovery.

For a period after the shooting, the boy was fearful and worried about everyone's safety, insisting they go look for his mother when she left the house. But he now understands when his mother is gone. He's playing sports again. A long vacation to the Grand Canyon this summer appeared to help the whole family.

Posey said his son also talks about becoming a detective who helps children.

Rojas said his son was excited to return to school this fall and see his friends but also apprehensive. Overall, he said, his son is "OK." He wishes someone could tell him everything will be fine in a few years, but he knows it will be a long road for his son and the other survivors.

"Not a day goes by that we're not thankful that we do have our son," Rojas said. "I think about our friends and neighbors who don't have that blessing anymore. Not a day goes by that I don't think about those 20 kids."