Global study links early smartphone ownership with poorer mental health in young adults

Maybe in adults, but I'm not so sure for early development. This topic was discussed on The Happiest Labs with Dr Laurie Santos and was pretty interesting. The psychologist she brought on explained how mammals need play as part of practicing socialization and is crucial for brain development.

The "play-based childhood" has shifted more toward a "device-based childhood" and the change is noticeable in many children's self image and executive functioning. Like this article mentions, the early access to social media seems to be the biggest contributor lowering self worth due to constant comparison.