It's important to understand causation. Engaged parents will still want to spend quality time with their children either way, but they will still want to know the impact. Even engaged parents let young children play with toys on their own from time to time. How are physical toys different than touchscreen "toys"?

A better way to put this is that the causality, if any, is unclear. However, it's very difficult to construct an ethical study on human participants that is designed to show causality. So we're usually left with, at best, a moderately rigorous abductive[1] conclusion.

[1] https://en.wikipedia.org/wiki/Abductive_reasoning