This situation has been well known for
years. It isn't news to any of us.
So why aren't we learning more about the problem? Why are we just beating the same dead horse instead of investigating further?
There is no way you could just convince the majority of children (or their parents) to just stop using mobile computers. Is there a more direct approach that could be taken?
Most of the comments here can tell you from experience: a computer is no more or less than a tool. It is what you do with it that matters.
Most of us here are critical of commonly proposed solutions to this problem, because they are so broad that they would disallow the beneficial activities that any motivated person can pursue with this tool.
If my parents had arbitrarily limited the time I was allowed to use a computer, I would not have learned even a tiny percentage of what I did.
If my parents had obsessively watched over my shoulder or limited my DNS access to exclude sites like Reddit, then I would have gotten repeatedly stuck early on, and probably given up on the very exploration that made computing a healthy part of my life.
We aren't talking about real computers, though. This is the brave new world of "smart phones". 30% of that market are Apple's walled-garden pretends-it-isn't-a-computer bricks. An unknown but significant percentage of Android bricks have permanently locked bootloaders. Even if a child is motivated to explore the subtleties of computing, chances are their device won't allow them to.
What if we put more effort into positive change? What if instead of trying to restrict a child's behavior, we did the opposite? What kind of opportunities are missed by the average child-available computing device? What opportunities should be made more approachable to an uneducated explorer? When I think about this problem from this perspective, I am overwhelmed with potential solutions. I would rather start trying those out than keep whining about the same old unsolvable problem domain.