It's not just kids who are overdoing screen time. Parents are often just as guilty of spending too much time checking smartphones and e-mail — and the consequences for their children can be troubling.

Dr. Jenny Radesky is a pediatrician specializing in child development. When she worked at a clinic in a high-tech savvy Seattle neighborhood, Radesky started noticing how often parents ignored their kids in favor of a mobile device. She remembers a mother placing her phone in the stroller betwe...