According to research in Canada and USA, as well of the recommendations of the OMS, infants should not be exposed to any electronic screen.
Children between 2 and 4 years old, should not exceed of one hour of sedentary screen each day children older than 5 y ears old, should have not more than two hours of recreational screen time.
Older toddlers and preschoolers if expose to screen time this should be mostly educational material, and music to reinforce some educational activity provided for an educator or a parent.
So, What parents and caregivers can do? Limited especially cartoons and movies, always watch with them the program, especially the new ones, and be special vigilant for the ads.
Remember that young children has short attention span so do not expose to long movies even if they are PG rated.
Encourage outdoor activities and play, exploring, wondering, listening to music and stories and encourage play. Daily Physical activity is very important for their development, so Reinforce exercise, sports, yoga.
How to tell when is too much screen time? When you notice your child nervous, lonely, overly tired, fearful, isolated from friends, angry, and with difficulty to concentrate.
Younger children learn for the interaction in the real world and exploring it.