That's how I grew up in a family of four in India and my parents are surgeons so we didn't really have them able to take us places for the majority of time. TFR at the time was 4.0 and we had access to contraception etc. and the majority of our trips here in SF are on foot as well. There are therefore some hidden assumptions here. We do take the car to the paediatrician etc. but I should soon have an Urban Arrow / R&M bike and will see how it performs.