It's not the quality of the show or the content that matters. Have you ever put a small child in front of the TV? It's like turning their brains off. To be honest it's quite startling.

It doesn't matter if its "wholesome" content or not - there is a physical decreases of core brain activity as the child disengages from the world.

I'll tell you that even at 4 I see differences in my son's behavior if he watches Turtles or if he watches something like Puffin Rock.

This point is actually acknowledged in the study findings under "Strengths and Limitations":

A limitation is that the information we collected did not allow us to separate educational screen time from other types of screen time. Doing so may have helped us in examining the association between screen time and child development while considering both positive and negative aspects of screen time.

The original data used in the study did not allow this differentiation but these findings can be used as a starting point for further research.