Jama Pediatrics has released a study showing that children who have more electronic screen time have a lower amount of structural integrity of white matter tracts in their brain. These support the language and literacy skills, as well as impact self-regulation and executive function. The children also on average scored lower on language and literacy tests. The American Academy of Pediatrics recommends that children under 18 months should avoid any screen time, and children ages 2-5 should only be looking at a screen for up to one hour a day. A suggestion to help keep screen time minimal is to have specified times without looking at electronics, such as during meals or in the bedroom.
Source: https://www.sciencedaily.com/