A new advert for a charity has turned the tables on the typical 'back to school' necessities in the US.

It begins by showing young children getting ready for school with new bags, binders and shoes.

But it soon becomes apparent something is wrong.

One student says: "My parents got me this skateboard I wanted, it's pretty cool" - before smashing a window to get away from a gunman.

The ad turns darker, showing students hiding as gunshots ring out.

One student, tending to a bleeding classmate, suggests: "These new socks - they can be a real lifesaver".

Young children are seen hiding in the video | Image via @sandyhook on Twitter

Another student is shown hiding in a bathroom texting 'I love you mom', before tearfully telling the camera: "I finally got my own phone to stay in touch with my Mom".

Footsteps are then heard coming towards her, as the advert fades to black.

"It's back to school time and you know what that means" it says.

The ad is from the Sandy Hook Promise - a non-profit organisation founded, lead by several family members whose loved ones were killed at Sandy Hook Elementary School in December 2012.

A gunman shot and killed 20 children and six adults at the school.

The shooter murdered the children and staff with a semi-automatic rifle, before taking his own life.

The charity says it wants to "honour all victims of gun violence by turning our tragedy into a moment of transformation by providing programs and practices that protect children from gun violence.

"By uniting people of all beliefs and backgrounds who value the protection of children to take meaningful actions in their homes and communities, we will prevent gun violence and stop the tragic loss of life."

It says the US has had 1,316 school shootings since 1970, and these numbers are increasing.

Some 18% of school shootings have taken place since the tragedy at Sandy Hook.

The school in Newtown, Connecticut was demolished back in October 2013.