I wonder if there's been any studies that compared children who do and who don't have access to screens, and then accounted for confounders. It's possible that secioeconomic factors need to be accounted for. It would be interesting to see this sort of analysis.

I wonder too if it is about the quality of the screen time, not just the quantity.  For example, my 2 year old has learnt the alphabet and counting from 1 to 10 through looking at an educational show on Netflix.  I think the author Alicia Lieberman who wrote "The Emotional Life of the Toddler" also comments on the fact that this is a complex issue.  If you watch something together and talk about it, it can be a bonding experience, but I agree that too much does not seem like a good idea.

The article notes that "these tests included measures of their communication skills (for instance, forming full sentences), gross motor skills (running and walking), fine motor skills (tying shoelaces or copying letters), as well as problem-solving, and personal and social skills (serving themselves food)."  While screen time may enhance communication, I can see where screen time could delay gross and fine motor skills (watching a screen does not teach a child how to run, jump or squat, cut paper with scissors or to handle a pencil) and it might delay some social skills because a screen is one way communication with no feedback.   I spend a good deal of time with children in recreational activities and I am finding the physical literacy is lacking more in children now than 10 - 20 years ago.  if this is related to screen time - I really do not know.