His neighborhood had no kids playing outside, so his kids didn't want to play outside. He did something about it, and he tells us how to do the same where we live.
The idea of solving this issue at a societal level is really daunting, but Playborhood was an empowering read as a parent. It makes the case that, at least for your children and your (hyper-local) neighborhood, you can create conditions that significantly change your kid's childhood (and mental well-being) for the better. And it provides actionable steps and examples to do that, rather than just bemoaning the state of the world.