Earlier quoted context omitted.
> Many people can't drive (minors, elderly, handicapped, health issues, etc.), and we still shade a ton of money on car infrastructure. Most of those who can't drive also couldn't get very far on a bike on their own. They can, however, ride in a car (or bus) driven by someone else, making use of that same infrastructure. Bikes are not typically designed to carry passengers.
Most people between age 7 and 16/17/18 can ride a bike, but not drive a car. Younger children can be a passenger on a bike.
In most of the US 16-year-olds can get a full driver's license and drive a car on their own, assuming they have access to one. Most parents these days wouldn't let a 7-year-old travel far without a chaperone by any mode of transportation even if they are physically capable. (Lack of "safe" biking infrastructure is far from the only risk factor.) But yes, in the very short window in the early teens between not being trusted to be out on your own safely and acquiring a driver's license and car a bike can be more accessible when traveling solo or with others of similar age and maturity.
> Younger children can be a passenger on a bike.
One younger child can be a passenger on a bike, at the expense of extra effort on the part of the rider providing the propulsion. Perhaps two if they are both small. (Don't forget that you'll need to bring extra cargo as well—especially if the passenger(s) are very young.) Beyond that you're going to want a larger vehicle with its own power supply, unless your goal has more to do with riding bikes than getting to your destination.