The UK’s Gambling Commission believes stronger efforts are needed to protect children from gambling, according to a new report it published on Wednesday. The study found the number of kids ages 11-16 classified with a gambling problem has more than quadrupled in the last two years, and video game loot boxes might share some of the blame.

About 14% of 11-16 year olds in the UK — approximately 450,000 of them — spent their own money on gambling in the past week, up from 12% in 2017, according to the study. About 39% said they spent their own money on gambling within the last year. An estimated 31% said they’ve opened loot boxes in a video game to try to acquire in-game items like cosmetic skins, while 3% said they’ve wagered with those items on skin betting sites. The Gambling Commission believes the ability to convert in-game items to cash, or to trade them for other items of value, gives them a real-world value, and it said it’s taken action in the past against unlicensed websites using in-game items as methods for payment.

“Protecting children from the harms that can come from gambling remains one of our highest priorities. In the areas we have regulatory control, we continue to strengthen the protections in place to prevent underage gambling, such as our recent proposals for enhanced age verifications checks for online gambling,” said the Gambling Commission’s executive director, Tim Miller.

“But regulation alone cannot address all of the risks that young people may face from gambling. Our latest research shows that the most common forms of gambling by children do not happen in gambling premises. Some of these are legal, such as bets between friends; some of these are unlawful, such as gambling on machines in pubs. But all of them present risks to young people as there is no form of gambling that is risk-free. It is therefore vital that all those with a part to play in protecting children and young people – parents, businesses and regulators — work together.”

Video game loot boxes have faced a lot of scrutiny over the last year in various countries. Fifteen gambling regulators from Europe, along with the Washington State Gambling Commission, recently signed an agreement to work together to address what they called “risks created by the blurring of lines between gaming and gambling.” Belgium, meanwhile, banned loot boxes and threatened legal action against video game publishers if they didn’t comply. A study by the Netherlands’ Gaming Authority found four out of 10 loot boxes violated its Betting and Gaming Act, and publishers were forced to modify their titles there as well.