Avoid digital media for toddlers younger than 18 to 24 months other than video chatting. For children 18 to 24 months, watch digital media with them because they learn from watching and talking with you. Limit screen use for preschool children, ages 2 to 5, to just 1 hour a day of high-quality programing, and watch it with them so you can help them learn from what they're seeing. See Healthy Digital Media Use Habits for Babies, Toddlers & Preschoolers.
Personal Note: Healthychidren.org has a wonderful series of advice for parents. I have saved each of them and have made them available at this link.