David, a 46-year-old father from Calgary, Canada, initially did not see a problem when his 10-year-old son started to play on Roblox, the platform of user-generated games and virtual environments that has exploded in popularity in recent years, particularly among younger gamers. “We saw it as a way for him to maintain a level of social interaction during the Covid lockdowns,” David said, assuming his son was using the platform’s chat function only to speak with friends he knew personally. After a while, his parents found him speaking to someone in his room in the middle of the night. “We...