WARNING: Some readers may find the details in this story disturbing.

TORONTO -- A new anti-gun violence PSA being called “chilling” and “powerful” online features children using common back-to-school items for self-defense during a school shooting.

Titled “Back-To-School Essentials,” the video has been viewed millions of times on Twitter. It shows elementary-age students showing off their new classroom basics, including backpacks, binders, and scissors. While the words echo typical school-year advertising language, the images depict a school shooting unfolding in the background.

“Survive the school year with these must-have #BackToSchool essentials,” wrote the Sandy Hook Promise Twitter account Wednesday morning. The non-profit was co-founded by parents of children who were killed in the 2012 Sandy Hook Elementary School Shooting.

In the video, a boy runs down the hallway as fellow students scream and fall in the background. “These new sneakers are just what I needed for the new year,” he says. A girl uses her “must-have” jacket to tie a knot around gymnasium doors as shooting noises echo behind her. Another boy uses the “pretty cool” skateboard his parents bought him to break through a window. A girl holds a pair of scissors in self-defense as more gun sounds are heard in the halls: “These scissors really come in handy in art class,” she says. A girl also ties a makeshift tourniquet around her bleeding classmate’s leg: “These new socks, they can be a real life-saver,” she says.

In the disturbing end to the video, a girl texts her mom “I love you” as she hears footsteps approach her hiding place. “I finally got my own phone to stay in touch with my mom,” she says through tears.

Co-founder Nicole Hockley, whose six-year-old son Dylan was killed in the 2012 shooting, has been a prominent voice in the post-Sandy Hook anti-gun movement. In an interview Wednesday on CNN, she explained her motivations for continuing her work with the non-profit today, including promoting the new PSA.

"I have to honor the son that died, and I have to protect the son that survived,” she said.

The video has been widely shared on Twitter, including posts by U.S. gun reform figures. “Our children shouldn’t have to live like this,” wrote U.S. Senator Elizabeth Warren on Twitter.

“Incredibly powerful,” echoed U.S. Senator Kamala Harris. “We don’t have to accept this as normal.”

“Chilling, heartbreaking & difficult to watch,” wrote U.S. Senator Richard Blumenthal. “We must take action so our kids do not have to go #BackToSchool fearing for their lives.”