One afternoon in September 2016, 7-year-old Ava went out into her South Carolina schoolyard for recess with her first-grade class. A local teenager in her poor, White, rural community drove up and started shooting at the children. After 12 seconds his .40 caliber pistol jammed, ending his attempt to become one of the nation’s youngest mass murderers. He threw the gun away and waited around to be arrested. Tragically, one of his shots killed a 6-year-old, a classmate whom Ava loved.

The aftermath of the shooting was also tragic. Many children in the school, including those who had not directly seen the violence, struggled with sleeplessness and nightmares, and had an incessant fear that the imprisoned gunman would somehow return. Many had headaches and stomachaches, along with separation anxiety. One lost the ability to control his bowels, another refused to go anywhere unless someone in his family took a gun, some went back to sucking on pacifiers. Kids had bouts of anger that their parents had never seen before.

Ava was among those with the worst reactions to the trauma. A shooting that lasted just 12 seconds began consuming every single one of hers. She had been a little girl brimming with creativity, curiosity and empathy. Now her life became filled with long stretches of quiet anguish and bursts of rage. Her severe post-traumatic stress disorder and depression made her unable to concentrate and interact effectively with peers and teachers. To her parents, she was a child they hardly understood, whose moods they couldn’t predict and whose agony they couldn’t fathom.

Washington Post reporter John Woodrow Cox witnessed one of her meltdowns. “In more than a decade of reporting,” he writes in his new book, “Children Under Fire: An American Crisis,” “I had never witnessed anything more unsettling than what happened that day. . . . The pitch of her screams, the intensity of her fury, it was like nothing I’d ever seen.” She is on medication, being home-schooled and constantly needs to wear headphones to avoid loud noises, one of her triggers.

“Children Under Fire” explores the effects of gun violence on American children. It delves into gun suicide, campus lockdowns and school security, and other gun-related issues, but at its heart lie the stories of specific children. What comes across with tragic clarity is that kids suffer terrible collateral costs from gun violence — and that suffering is too often overlooked.

To illustrate the profound impact, Cox focuses on the struggles of two kids, Ava and a 7-year-old boy named Tyshaun. For Ava, her episodes, the torrents of rage she experiences, have come to define her life. She cannot stop herself, though she tries. She explodes again and again, slapping herself, screaming obscenities, writing expletives, banging her face against a wall. She lives in perpetual fear that she is going to lose those closest to her, that she will inevitably do something to drive them away, but she cannot control herself. Her little brother says, “I miss her being happy.”

Tyshaun developed many of the same PTSD symptoms as Ava after a family member was slain. Just a few months after the South Carolina killing, Tyshaun’s father was shot to death in his poor, minority community in Southeast Washington, where gun violence is prevalent and trauma affects the whole area. Sufficient medical treatment for that trauma is lacking. Like Ava, Tyshaun has been unable to control his PTSD symptoms.

Chronic exposure to violence can disrupt a child’s brain development and inflict profound mental harm — depression, anxiety, sleeplessness — and uncontrollable anger. PTSD can lead to hypervigilance, and kids in that mind-set often mistakenly believe they have to defend themselves, so they lash out, leading to school discipline that can exacerbate the underlying problem. PTSD makes them emotionally guarded, and the held-in grief, shame and rage readily spill out.

Hurt people in turn hurt others, and it is difficult to find needed support when so many in the community are traumatized. The scholarly evidence that exposure to violence — particularly gun violence — is a risk factor for emotional and physical health problems throughout one’s lifetime is now overwhelming.

Intriguingly, after Cox wrote about Tyshaun’s problems in a Post article, Ava wrote to Tyshaun, and they have become strong video chat friends. Tyshaun is gentle with Ava in a way that his mother had not seen since his father’s death, and Ava is comfortable with Tyshaun in a way her mother had not seen since the school shooting. “We went through the same thing,” Tyshaun explains, “losing somebody that we care about, and we like to chat a lot, and we both know how each other feel when we get emotional and stuff.”

Compared with our peer countries — more than two dozen other high-income democracies — the United States has similar rates of non-gun crime and violence. But we have the most guns and the most permissive gun laws. Not surprisingly, our children are dying from lethal violence at rates far exceeding those in every one of these other countries. I teach in a public health school with many international students. They know what is happening here, and none can understand why American adults refuse do something about it.

My academic injury-prevention center has conducted many surveys of students in U.S. cities, including Washington. The teens tell us that it is easy to get guns and that many have carried guns (illegally). The main reason they carry guns is because they are afraid, and they are afraid because other kids are carrying. We ask them if they would like to live in a world where it is easy, difficult or impossible for teens like themselves to obtain guns. The overwhelming majority — even most of those who admit to illegally carrying — want it to be impossible. That is the world in which urban teens in virtually every other high-income country live — where adults have made it virtually impossible for adolescents to readily obtain a handgun.

I have been analyzing and writing about gun violence statistics for more than three decades. I have learned that while data and analyses are crucial for policy change, so too are stories like those of Ava and Tyshaun.

“Children Under Fire” is an important book and should be read by as many people as possible. But I found it hard to read because I really got to like these children, and it is clear that because of a few seconds of gun violence, their life journeys have become difficult and may not be successful. It is also clear that until we as a country begin to protect our children, like adults in every other high-income country protect their children, there will be thousands more Avas and Tyshauns each year whose lives are shattered by our aberrant gun policies.

Children Under Fire

An American Crisis

By John Woodrow Cox

Ecco. 328 pp. $28.99