> For babies research has shown that screen time is undifferentiated.

The research is largely undifferentiated, and overwhelmingly (maybe even entirely, for good ethical reasons) is observational studies that, even if they were able to distinguish between a differentiated relationship and an undifferentiated one would be unable to distinguish between, in <1 year olds, screen time causing developmental delays and conditions which cause developmental delays also causing behavioral differences which lead parents who respond to how things affect their children's behavior to be less likely to curtail screen time.