As much as I hate cars, it's not just the cars, but also the social isolation that is a signature of urban environments.
My kids spend a lot of time at the neighborhood park, as one example. It's within walking distance and we see a ton of families there. Density (with infrastructure like parks) creates opportunities for connection.
(1) from the Wikipedia article you cited, "Reid Ewing has shown that sprawl has typically been characterized as urban developments exhibiting at least one of the following characteristics: low-density or single-use development, strip development, scattered development, and/or leapfrog development (areas of development interspersed with vacant land)"