A new report found that the amount of time young children in the United States spend with mobile screens has tripled in just four years. Jenny Radesky, an assistant professor of developmental behavioral pediatrics at C.S. Mott Children’s Hospital, wrote a commentary in the new report and offers some screen time tips for parents. According to Radesky, infants and young toddlers usually don’t have the symbolic thinking or memory skills to understand two-dimensional screens until they are around 15 to 18 months old. “I tell parents not to stress if they want to watch a sports game now and then with their baby — or they need to put their older infant in front of PBS for 20 minutes while they do the dishes — but keep it short, understand the realities that media is not educational at this age, and avoid a lot of background TV when no one’s watching. We talk to our kids less when it’s on,” she said. Radesky was also lead author of the American Academy of Pediatrics‘ recommendations for media use released last year.