bright young thing

A bright young thing is a fashionable, lively young person, especially one from a privileged background who's part of a glamorous social scene.

The phrase originated in 1920s Britain describing wealthy, hedonistic youth who frequented parties and nightclubs: She ran with the bright young things of London society.

Now used more broadly, sometimes ironically, for any promising or attention-getting young person: The magazine profiled the bright young things of Silicon Valley.