They usually suffer from anxiety and sleeping disorders, attention deficit issues and even depression and eating disorders.

The World Health Organization agrees: earlier this year it said "gaming disorder" would be added to its compendium of illnesses.

Sport can be an important part of treatment.

"Physical activities such as martial arts are very good for children to help them get healthy entertainment and meet friends," said Minh.

Strict schedule

IVS was set up in 2009 by Vovinam Master Pham Quang Long to treat unruly youngsters aged from 13 to 19.

There are around 1,000 kids enrolled at all five IVS campuses, where tuition costs about $330 a month and pupils are allowed a visit by parents once a month.

Students must adhere to a strict schedule from dawn until bedtime around 10 pm that includes academic courses, music lessons and physical exercise.

Most days, that includes Vovinam.

Early Vovinam protagonists were inspired by nationalist movements during the French occupation, eager to learn self-defense and develop a uniquely Vietnamese martial art.

But the sport was forced underground in the 1950s by French rulers who wanted to extinguish nationalist sentiment of any kind.

It reemerged in the 1970s, eventually becoming a global movement. Today, there are Vovinam federations all over the world.

Agence France-presse