I barely remember what it was like waiting for the bus with nothing else to do. But I remember vividly what it was like that the school bully was next to me waiting for the bus with nothing else to do. Hope my kids don't have to know what thats like.

My point is not that smartphones and social media are great things. But I agree with OP that they are just filling a gap created by something else. It is still possible to be bored or have time solely with your own thoughts with social media available. Why? Because even kids can (and do) understand that social media is not all that great. Of course they have to experience that on their own before they understand it. It's nothing that you can teach them.