About 60 Hong Kong parents on Sunday launched a protest against advocating politics on local campuses, saying it could "brainwash" their children and affect their academic performance.

They took to the streets as some secondary students in the city boycott classes and launch human chain campaigns on campuses to press their political demands. The parents marched from Chater Garden in Central to the Central Government Offices in Admiralty, chanting "oppose brainwash, keep campuses away from politics" and "children are not teachers' pawns".

The Education Bureau had earlier issued warning letters to two teachers who had written offensive words against police officers on their social media accounts. The police arrested a 13--year--old boy for various offenses, including possession of offensive weapons in public, and a 13--year--old girl who burned the national flag, during two violent protests on Saturday.

A total 15 other juveniles, aged between 12 and 15, have so far been detained for suspected roles in protests against the now--abandoned extradition bill from June to late August, according to the police.

Ouyang Haixuan, one of the conveners of the demonstration, has a son attending a local primary school. She said she opposes campus politics in order to protect his son and other children from the political turmoil and ensure that children have a peaceful and safe environment to study.

"Seeing secondary students in school uniform forming human chains and chanting political slogans after the new semester started, I doubt whether they clearly know what they want. I'm worried whether they realize their priority is to study hard," she said.

As a mother, Ouyang said she's disappointed with Hong Kong's education system. If the chaos continues, she said she would get her son to leave the chaotic environment and study on the Chinese mainland.

Jackey Ko, 40, a music teacher, urged school teachers to behave in strict accordance with work ethics and the professional spirit, and to avoid expressing their political views in front of students.

Concerned about his 17--year--old son being bullied in social media groups involving classmates, and subject to political wrangling on campuses and in society, Ko decided to send his son to study overseas a year earlier than previously planned.

"I hope he (my son) can grow up in a harmonious society," he said.

Renee Leung, a mother of two underage sons, told China Daily she's firmly opposed to bringing politics into campuses.

Juveniles, especially kids in primary and secondary schools, have yet to develop a mature outlook, and they are taught to follow the "authorities", including teachers and parents, she said.

Parents and teachers should provide appropriate guidance to help children develop righteous value systems rather than forcing their own opinions onto their children, Leung added.