At least 28 children have been killed in protests that have swept Iran since the death of Mahsa Amini, with hundreds more mostly detained in adult prisons, rights groups inside and outside the country said.
Amini, 22, was pronounced dead days after the notorious morality police detained the Iranian Kurd last month for allegedly breaching the Islamic republic's strict dress code for women.
Anger flared at her funeral and spread to become the biggest wave of protests to rock Iran in almost three years, despite a crackdown that has killed scores and seen hundreds arrested.
Iran's Children's Rights Protection Society condemned security forces for resorting to violence against children who have protested in schools and in the street.
"According to statistics, 28 children have been killed in these confrontations, most of which happened in the underprivileged province of Sistan-Baluchistan," the Tehran-based group said in a statement posted on its website Monday.
It criticised "families being kept in the dark on their children's whereabouts, cases proceeding without lawyers and lack of children's judges and police".
The group said the government "must be held accountable" and bring forward and punish "anyone, of any rank, who has been the cause of violence or harassment against children or their deaths".
Revolutionary Guards deputy commander Ali Fadavi told Iranian media on October 5 that the "average age of the detainees from many of the recent protests was 15".
"Some of the teenagers and young adults arrested used similar key phrases in their confessions, such as likening street riots to video games," the Mehr news agency quoted Fadavi as saying.
Human rights lawyer Hassan Raisi said some of the children arrested were being held in detention centres for adult drug offenders.
"This is very concerning," he said in a report posted on the London-based Iran Wire news website on Wednesday. Those "under the age of 18 must never be held with any criminal over 18... This is a legal requirement, not a recommendation."
He added that "around 300 people between the ages of 12-13 and 18-19 are in police custody".
Schoolchildren joined the protests soon after they began in mid-September, with girls removing their hijabs, shouting anti-government slogans and defacing images of the country's leadership.
The United Nations children's agency UNICEF said Monday it was "extremely concerned" over reports of "children and adolescents being killed, injured and detained" in Iran.