Youngsters, who say they were detained for more than six hours, launch legal challenge in high court

Metropolitan police officers illegally detained children as young as 11 for more than six hours during a "kettling" operation against tuition fee protesters, the high court has been told.

Three of those held last year are challenging the decision by senior officers to contain youngsters – some of whom were wearing school uniforms – among masses of demonstrators on Whitehall.

The case focuses attention on police use of the tactic to prevent groups of people moving through the streets. It has been criticised for its indiscriminate punishment of everyone present.

Lawyers for Adam Castle, 16, his sister Rosie, 15, and Sam Eaton, 16, all from north London, argued the police operation was unlawful because no release plan had been prepared to cope with the presence of children.

Martin Westgate QC, counsel for the children, said the police failure constituted a breach of their obligations under section 11 of the Children's Act and of their responsibilities to respect human rights.

The children had, with their parents' permission, joined the National Student Walkout demonstration against the rise in university fees on 24 November.

"The claimants were entirely innocent of any misconduct," Westgate said. "Other children were also prevented from leaving. One 11-year-old was told to 'get back' at a fairly late stage in the containment."

The "kettle" operation began at 12.30pm and children repeatedly presented themselves at the police lines asking to be allowed to leave. They showed Oyster cards and offered other proof of their age but were not allowed to depart.

"Children … were reasonably capable of being identified as non-violent participants," Westgate said. "There's no suggestion there were a significant number of violent children."

Radio logs of the police operation showed that officers feared some protesters had knives or, in one case, a gun. "It seems that the release took longer … because the police wanted to secure evidence for arrests," Westgate said. "That's not a lawful use of containment."

The children were among 10 friends who joined thousands of students, lecturers and teachers in Trafalgar Square to march towards the Houses of Parliament. Rosie was trapped for about six hours and the boys, who were in court, for seven-and-a-half hours.

Westgate said he accepted the decision to impose the kettle was lawful because of police fears breaches of the peace were imminent but added that the operation became unlawful because of the failure to have a release plan communicated to frontline officers.

Lawyers for the Met police argued that the containment had not been pre-planned, that there was no expectation that schoolchildren would join in and that provision had been made to help vulnerable people caught up in the protests.

Requiring the police to record every possible consideration in preparation for large operations would be a "sterile exercise", the force added. Two portable toilets were provided, but only five hours after protesters had been penned in.

Outside court Sam said: "I just felt like we were being punished for demonstrating, as opposed to us doing anything illegal."

Adam added: "I hope the judges see that kettling broke our rights. We were punished for protesting and everyone was left demoralised. It was one of the coldest days of the year and we had not been prepared for being held into the night.

"As children we can't vote, so one of the best ways for us to voice our opinion is through protest and if that's stopped or inhibited by kettling then where are we left?"

His sister Rosie was released earlier and separated from her brother. Adam said: "She knew where she was, but she didn't know how to get home. She didn't expect to be separated and left out in the middle of London in the evening. No one was prepared for that."

The hearing continues.