The cities mentioned as being great for cyclists are Copenhagen and Amersterdam, and now Berlin is trying. What is interesting is that the countries these cities are in Denmark, Netherlands, and Germany have fertility rates of 1.7, 1.7, 1.5 births/female [0]. In other words, people aren't having that many children. When transporting children, cars become a whole lot more convenient than bicycles. You don't have to wo…
I have family in Germany and they have two young children. They own a car but they only use it occasionally for trips. Their daily commute involves one of the parents transporting children to or from kindergarten using a bicycle trailer that both children can sit in. They do this year round and it works out fine. It works out a lot better, in fact, because cycling is much faster than sitting in rush hour traffic.
It is very much a cultural thing in my experience. Nearly all children go to primary and high school on their bicycles, by themselves, although the trips for high schoolers are often I think that touches on why it might not be as popular in other countries, as other countries might not be as flat or lack city planning that takes cyclists into account, e.g. dedicated bike lanes.
It’s also an excellent choice for a country of our size that has limited space, as bicycles make much better use of it than cars.