Sandy Hook shooting victims' advocacy group airs chilling anti-school violence ad

WARNING: THIS VIDEO CONTAINS GRAPHIC CONTENT.

[Upsound video]:

“This year, my Mom got me the perfect backpack for back-to-school….”

It starts out like a typical ad for back-to-school gear...

[Upsound video]:

“These headphones are just what I need for studying….”

but quickly turns into a spine-chilling warning about what is now the new reality for children in America – gun violence at school.

[Upsound video, laced with children's screams]:

“My parents got me the skateboard I wanted. It’s pretty cool.” [smashes window]

The public service announcement, released Wednesday, was created by Sandy Hook Promise, a non-profit group led by family members of children massacred at the Sandy Hook Elementary School in Newtown, Connecticut in 2012.

Airing on NBC's "Today" show Wednesday and online, it aims to bring awareness to the organization’s school violence prevention program "Know the Signs," which teaches kids and adults how to recognize warning signs and intervene to prevent mass shootings.

Scenes from the PSA heartbreaking and harrowing.

[Upsound, video, of girl crying]:

“I finally got my own phone to stay in touch with my Mom.”

A gunman killed 26 children and educators at Sandy Hook, where the non-profit is based, in the deadliest public-school shooting in U.S. history.