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 has just been part of my life,” he says. “I feel raised by it a little bit.” ... Roblox has turned its tween audience into an army of fresh-faced entrepreneurs.