A 12-year-old boy who admitted spraying anti-government graffiti on a police station and a metro station exit was placed under a two-year care or protection order on Thursday.

The unnamed Form Two pupil is the youngest protester to plead guilty before the court during the more than six months of social unrest in the city.

Appearing at Juvenile Court of West Kowloon Magistrates' Courts, the boy was also given a clean record as criminal charges against him were dismissed by the court after his lawyer said the young offender had "learned an important lesson".

The protection order, with immediate effect, includes a curfew and compels the student to participate in designated social activities for the next two years.

The boy had pleaded guilty on Nov 12 to two charges of criminal damage. He was arrested by a police officer who saw him vandalizing the Mong Kok police station and an exit of the Prince Edward MTR station on Oct 3.

The defendant's lawyer, Jacqueline Lam Hoi-yee, asked the court for leniency, saying the boy has shown remorse and realized he had adopted an improper method to express his views.

Lam also said the student had committed the crimes on impulse and under the influence of other protesters he wasn't acquainted with.

Magistrate Pang Leung-ting accepted an assessment report by Social Welfare Department officers and decided to drop the charges against the boy under the Juvenile Offenders Ordinance, taking into account the fact that spray-painting is less serious than other acts of criminal damage.

In an earlier protected interview, the boy, whose parents are divorced and who has been living with his grandmother, said he was sorry for what he did.

More than 6,100 people have been arrested so far in connection with the prolonged anti-government protests that erupted on June 9. About 40 percent of them are students. A total of 978 have been charged as of Monday, mostly for rioting.