Parents have been caught helping their children bypass age checks and play as adults on Roblox, the gaming company has said, forcing rechecks on accounts deemed younger than they appeared.

In December last year, Roblox rolled out new features to prevent children from chatting with adults they do not know, by making users who wish to use the chat function pass through facial age assurance that then groups them in similar age group cohorts until they turn 21.

Since the shift, Roblox has monitored account behaviour to detect signs that the user might have been younger than the age they appeared in facial age estimation, with some parents being discovered in the process.

“When we went and did the validation tests on that, you could see the kid in the background who handed the phone to their parent,” he said. “So that’s why we have these systems in place,” said Matt Kaufman, Roblox’s chief of safety.

Kaufman said the facial age estimation systems aren’t perfect, with error rates in facial age estimation about 1.4 years for users under 18, and some users finding other ways around it.

“We want to make sure that people aren’t simply holding up a video of somebody else, or using a magic marker to put a moustache on their face and claim that they’re much older,” he said.

The company has extensive fraud checks in place, Kaufman said, to ensure the age check process is not being manipulated.

“Age checks [are] not a one-time process … if we notice their user behaviour doesn’t quite match up with what the age check process generated, we’ll simply ask the user to go through the process again.”

He said rechecks were happening every day for users.

As of April, 50% of Roblox’s global 144 million daily users have gone through age assurance checks. The figure is 60% in Australia, New Zealand and the Netherlands, where it was rolled out in December.

Roblox is currently excluded from the under-16s social media ban in Australia, following the introduction of the new safety features. Last month, the eSafety commissioner, Julie Inman Grant, confirmed that children were easily bypassing the facial age estimation technology deployed by the social media platforms if they were aged within two years of 16.

As of March, the commissioner had found more than two-thirds of teens under 16 in Australia were still on the platforms included in the ban, and half of the 10 platforms were being investigated for non-compliance.

The changes to Roblox followed a Guardian Australia investigation last year documented a week of virtual sexual harassment and violence on Roblox experienced by a user with a profile set up as an eight-year-old.

The company also announced it would bring in additional checks for games launched on the platform, including moderation that not only assesses the content of the game but how players interact with it, to ensure that it is appropriate for the age groups that are playing it.

Roblox has announced new account types for users under nine years old and for those aged between nine and 15 with age-appropriate games. The company also plans to begin using the Australian classification system for games later this year.