The Freakonomics guys are notorious for using shoddy research, jumping to bad conclusions, and generally publishing provocative conclusions just for the sake of provocativeness that don't hold up to even a whiff of debunking. I rolled my eyeballs through the entire book.
Good rebuttal of the car seat story here, with lots of links: https://thecarseatlady.com/freakonomics-fallacy-an-economist...