How old should a child be before getting their first cell phone? There’s only one correct answer if you want them to lead happier, more successful lives, says Yale University psychology professor Laurie Santos: “Wait as long as possible. I think the more we can hold off on giving kids technology — the longer, the better.”

A recent report found that children ages 8 to 12 who have phones spend just under five hours a day glued to their phones, and teenagers rack up nearly eight hours of screen time per day. That screen time is seldom used for creative activities like coding or making digital art. Rather, young people spend most of their phone time on social media or watching videos. This is likely to encourage poor mental health—in ways that affect kids differently than adults.

Social media use exposes many kids to cyberbullying, hate speech, and discrimination. Even YouTube videos meant for children can contain malicious, disturbing, or inappropriate content.

Just the sheer number of notifications a child might get from social media—probably more than their parents do—can be overwhelming. Santos says, “Teenagers are getting on the order of 200 notifications from their phones today. These are brains that are forming and trying to pay attention in school [while their phones are going] ding, ding, ding.”

Halting smartphone use for children and young people until they’re in 8th grade comes with benefits, including: Less risk of anxiety and depression, increased quantity and quality of sleep, and more time for physical activity and the outdoors

Parents should also lead by example, Santos adds: “If you’re constantly on your cell phone, it’ll be harder to justify why your child can’t have one. They’re not going to want to do as you say, they’re going to want to do as you do.”