New Jersey residents were left in shock after five children, aged between 10 and 11 years, were arrested for planning to explode a fake bomb in their school, US media report.
The alleged bomb threat on Clifton High School, with a total strength of around 3274 students and 230 teachers, was exposed after the teachers found a letter with the plan details and alerted the police.
Four girls and a boy on Wednesday had carried an "artefact" to their school, which they allegedly planned to detonate the same day, Channel 12 news in New Jersey reported on Thursday.
However, the "artefact" only contained vinegar and cinnamon, said NorthJersey.com website.
But the police believe the plan was not a prank and that the students wanted to "cause damage", although their motive is yet unknown.
"It was not a prank. They had a legitimate plan," said Clifton Police spokesperson and investigating officer Sgt Robert Bracken.
"They didn't have the right equipment, but the intent was there," Bracken added.
The children were suspended from school after being arrested and interrogated by the police, although they have not been formally charged yet and are under parental supervision.
The incident occurred hours before the San Bernadino mass shooting in California, which left 14 dead and dozens wounded.