Fifty-six million American children have just gone back to school after the summer holiday.

Their parents are being treated to an unusual TV ad - designed to shock them into realising why it's no time to breathe a sigh of relief.

It was made by the parents of a school, called Sandy Hook. It starts out like any other back to school ad, but it's certainly not - the sound of gunshots makes that perfectly clear.

The idea is to create a sense of terror students and parents live with every day, that their school could be next.

"This is what kids are experiencing today, and that's what we have to take action," ad campaign organiser Nicole Hockley said.