Don't give your kid a smartphone before high school, and don't let them use social media before age 16, New York University social psychologist Jonathan Haidt argues in a new book.

Why it matters: The shift from "play-based" to "phone-based" childhoods is making our kids sick and miserable, Haidt argues.

Driving the news: In "The Anxious Generation: How the Great Rewiring of Childhood Is Causing an Epidemic of Mental Illness," out March 26, Haidt says that staring at screens all the time is terrible for human development.

• A "phone-based" childhood causes "social deprivation, sleep deprivation, attention fragmentation and addiction," Haidt writes.
• A "play-based" childhood is essential for developing physical and social skills, like conflict resolution.