There is extensive research ongoing. Your question has two pieces to it. One piece of it is how parents can discourage the kids from using the screen time too much. The other one is about the long-term health consequences. I'm going to break it up into those two pieces.
On the first question, there are older studies that are continuously being updated that followed children from 1994 through 2011. Now they've stopped interviewing them, but they're following them administratively through census, education, the justice system, the health data system and all kinds of different data sources to look at the overall outcomes. They followed them for the first 16 years to understand how they were living their lives and how active they were. Now they're following them administratively to see where they end up, based on their earlier life choices.
With regard to the second piece, there is ongoing research as well to try to figure out how parents can reduce the screen time of their children. I haven't seen anything that seems to be the magic solution yet. I have three teenagers myself and I would be interested in that solution, but I've seen no concrete recommendations so far.