> Consider some statistics on the American childhood, drawn from children aged 8-12: 62% have not walked/biked somewhere (a store, park, school) without an adult

At least in the US, my guess for the cause of this is goes something like:

1. Housing is expensive.

2. People move to where housing is cheap (ie plenty of land, easy to build). In the last few decades that's more often than not been in the south.

3. Big population changes in those areas demand more schools.

4. Big school is built on the edge of town, because that's where the land is and one school has better economies of scale than multiple neighborhood schools

5. No one lives close to the school anymore, so everyone has to drive.

Throw in the sprawl that often accompanies new development in areas with wide open land and its easy to see how we end up here.

I live in Brookline, MA (in the North, next to Boston) and it's very much a walk-to-school town. The structural reason for that is our schools are in the neighborhoods, have been around for a long time, and there's nowhere "on the edge of town" to build a new one. Our town has financial pressures like everyone else and I few government's are able to resist the temptation of cost savings---we just don't have the option to build that way. Thank goodness.