You must live in a huge bubble if you really don't know anyone without a car who has kids. The majority of the parents that live near me don't own cars.
You know that you can take strollers on buses and trains, right?
The majority of parents that live near me own cars. Anecdata is kind of useless here.
In 2017, the American Communittmy Survey showed that of the 46m households with 3+ people, approximately 44 million had 1 vehicle and 16 million had 3 or more vehicles.
If you see two parents and a child in America, it's more likely one of them thinks the moon landing is a hoax than that they do not own a car.
Clearly it's not flat-out impossible to have children without a vehicle if millions of people are doing it, by your own stats!
And those stats aren't suitable for this purpose (they're undercounting my millions more), as there are many one parent households, plus many parents who live in a household with others but who don't own cars themselves.
2 person households, 38 million with 1+ cars, 2 million without.
4+ person households are almost as likely to have 4 or more cars as 0 or 1 cars.
Single person households are almost as likely to have 2 or more cars as no car at all. (The dominant number of vehicles by far is, of course, 1.)
Of the 85 million households with more than one person, only 3 million have no cars at all. You can "undercount" and adjust all you want, you're talking 5%, maybe 7% maximum of "parents without cars."
Of course it's possible, in a few scattered geographic areas with high density and convenient public transit. But that's not almost any of America.
You know that you can take strollers on buses and trains, right?