Millions of children have flocked to the online gaming site Roblox since March. That’s helping game developers, some as young as 16, make a lot of money. Garvey Mortley, 12, with her mother ...

Roblox hosts millions of games that are built by its users, who then get a share of any related revenue. Two thirds of all US kids 9 to 12 years use the platform, according to the company.