To the extent that "ban cars" even exists as a real political archetype rather than a meme, this is just patently not true. At least one of the two co-hosts of The War on Cars (again, a title which is intentionally tongue-in-cheek) has a preteen son.
But more importantly: car-dependent suburbs are an absolutely miserable place to grow up as a child if you're not wealthy enough to have one non-working parent and/or a nanny (or both). Being dependent on someone else to enable your entire social life until you turn 16 is a torturous enough experience that I'm not surprised that the first generation to have universal access to social media as teenagers has become the first generation to use social media to organize a teenage-driven movement for public transit.