Australian families are being hit with hundreds – sometimes thousands – of dollars in losses as online scammers prey on children through Roblox, luring them with fake offers of free in-game currency.

The creator of “Blue Lock: Rivals” thought kids on Roblox might like a soccer video game with an anime vibe. It sold a few months later for more than $3 million. The 19-year-old, who asked that his ...