The boy was receiving treatment in hospital for an “illness”, police said, without giving further details.
Protesters were charged with various offences including unlawful assembly, possession of an offensive weapon and assaulting police officers.
An Assistant Commissioner of Police, Mak Chin-ho, on Monday, defended police actions, saying that the use of force was necessary to quell increasing violence.
Mass protests began on June 9 against a legislative bill that would have allowed for criminal extradition to mainland China, which has a separate legal system from Hong Kong.
Many Hong Kongers have broader fears that their special status is under threat from Beijing.
Chin-ho also condemned the damage to smart CCTV posts, which protesters tore down on Saturday in eastern Kowloon.
“Their destructive acts are rampant and reckless.
“They are not tolerated by any civilised society,’’ he said.
The chaotic weekend saw protesters throw rocks and petrol bombs at riot police from behind barricades assembled on major roads in the Kowloon peninsula.
Late Sunday, a group, armed with bamboo poles also clashed with riot police, prompting six officers to draw their guns and one officer to fire a warning shot.
“I must emphasize the officer demonstrated great restraint,’’ Chin-ho told reporters.
“Their use of force was indeed necessary and reasonable, it was to protect every person including our officers themselves from death and serious bodily injury.’’
Police deployed a water cannon for the first time on Sunday and used extensive tear gas over the weekend in an attempt to disperse crowds.
Forty-eight people were also injured over the weekend, according to Hong Kong’s Hospital Authority.
Edited by Abdulfatah Babatundehttps://nnn.ng/12-year-old-among-86-arrested-during-weekend-protests-in-hong-kong/