This comment is for the Police Warning message:
Please check these kind of things with urban myth sites such as snopes.com or similar before passing it on and worrying people. Your concern is understandable but, as with many similar stories like this, it is false. See, http://www.snopes.com/crime/gangs/carseat.asp
This story, or very similar, has been doing the rounds in numerous countries since at least 2009. It has been dismissed as a hoax by law enforcement agencies across the world.