Is having more than one car per family relevant to the question of whether having kids implies having a car?
In any case, it looks like the answer is more or less "yes." The difference in car ownership per capita is not that different between the US and many other first-world countries:
But this counts a lot of vehicles we wouldn't consider "cars," like tractor trailers. If we just look at passenger vehicles, it seems that the US is nowhere near the top:
So not only is the US not unique in being in love with cars, we're not even the most excessive at it. Maybe the next time somebody feels like getting all nationalistic about criticizing car culture, they'll point the finger at Italy, Germany, or France before they decide to aim for the US.
The Carnegie data at least was put together for the purposes of making a point about the size of the middle class and I believe a number of those pieces, in addition to The Atlantic, are making use of that data set.
From the comments to that article, there seem to be some questions around what vehicles exactly are being counted and whether the methodology is consistent from country to country (e.g. pickups are probably quite a bit more common in the US than in western Europe). You could also argue that per capita isn't really the best measure and you may consider adjusting for income measures, demographics, and urbanization.
That said, there's a stereotype of Americans as a car culture where people drive everywhere and western Europeans as living in the core of medieval cities and walking/biking/taking transit everyplace. And that stereotype doesn't hold up.
