Majority of those are largely solved with good city planning and other regulations around cars, including a healthy amount of drivers ed as well as actually taking away people's license for repeated or severe offenses (note I said or, not and - either one should be enough). I drive a car, so does pretty much everyone else on my street, and yet children do play on the street, much like we did 25 years ago when I was a kid here (there are fewer kids, but that's a different issue entirely, we've had low birth rates since the 90s or 00s). Keys: Narrow street, very few American style pickup trucks (There's an Amarok someone on the street uses as a work car and that's literally it). The speed limit is technically 50 km/h because there's no specific speed limit set on this street and it's not marked as a "living street", yet you almost never see anyone go that fast. We don't even have a speed bump because it's just not been necessary. Both entries into the street have you come in at low speed.

Both here in my small town and in the country in general, it's fairly common to walk or bike to school. Usually the main thoroughfare of any suburb or town has a wide sidewalk on one or both sides, and side streets tend to be narrower and potentially limited to 20 or 30 km/h and since there's often no sidewalk on those, the DEFAULT assumption is that there will be pedestrians and cyclists you share the road with. The law also states that in close proximity to pedestrians, you have to slow down to near-pedestrian speeds (not exactly defined and since cops love giving out tickets, you'd better err on the safe side).

Air quality will be a mostly solved issue once EVs are as cheap to buy as used diesel cars too, they're certainly cheaper to run already if not accounting for purchase cost. Petrol doesn't pollute nearly as badly locally as diesel does, it's worse for global warming though (CO2 tends to be higher). But for now of course it is indeed sad we breathe in toxic fumes.

As for play at night, that's just illegal here, kids have a curfew starting at 11 PM (or midnight in the summer), after which they can only be outside with their parents or guardians. Like... let's be honest, do you want your kids out without an adult after that time? Even if there's no cars, guess what else a walkable city is conducive to - alcoholics wandering around. And yes, if you've grown up with them, you know to ignore them, but maybe one out of a hundred is still dangerous occasionally when in a bad mood.

Anyway I know this is fuckcars, but you CAN achieve much of this without outright banning cars and honestly it's nicer as a driver too. I was in the US for a week a few years ago and while I was able to walk to some of the places I needed to (in a small town of ~20k in upstate NY because I was visiting relatives), I found it easier to take the rental car to most places. Yay V8 SUV powered grocery store runs (hey, we were in the US, we wanted to test what it's like to just guzzle fuel without giving any fucks since it's so cheap). Not how I feel in Estonia, where I've never lived farther than 1 km from a decent grocery store I could safely walk to. If the weather's nice and I'm not in a hurry, I'll just walk to the store unless I know I need more stuff than I can carry. Much of the time I'm in a hurry because my own life is super busy lately, so I'll drive, but since so many other people walk, cycle or take transit, you only really see traffic jams at rush hour and only in the bigger cities and even then they're not very long.

Honestly feel like 99% of American cities are designed to be frustrating to everyone involved. Walk or cycle? Die being hit by a car because there's no fucking sidewalk, let alone cycle path. Drive? Die of boredom in traffic jams because EVERYONE is driving and cities are designed like shit. NYC was awesome though, even if the subway train sounded like it had nearly derailed in every sharp turn (and those were some sharp ass turns for something on rails).