Kids are being identified as adults—and vice versa—on Roblox, while age-verified accounts are already being sold online.

I traveled to Roblox's headquarters to do a demo of a new safety feature it says will help protect child users.

SAN MATEO, CA — At first, the messages seemed normal. Innocent, even. “Hi,” “How are u?” And then: “Do you want to make Robux?” To millions of kids who play Roblox every day, those words might seem ...