OP, your opening post comes across as very right wing about this issue, and by that I mean you've got an idealistic idea of how nice it would be and how good for everyone if all families walked to school every day.
Yes, it would be lovely and I'm sure we'd all be healthier.
The thing is, it isn't always that simple.
We live about 1.7 miles from school (or is it 1.4 - can't remember) and it's a horrible walk, along a very busy road with very narrow pavements so if you randomly stick your arm out a bit at the wrong time, it will get cut off by a bus.
It's up a long hill
There isn't another feasible route
We do it sometimes, but that means a long walk back for me afterwards, and if we did this at both ends of the day it would mean about six miles of walking for me.
I don't mind the idea of that - in fact I share your idealistic vision - but realistically, it would mean I had neither the time nor the energy to do anything once I got home.
I have to do everything myself here - all the shopping, all the DIY, (there's a lot - we are renovating) and looking after a huge garden and 8 pets. Plus two lively children and another on the way. (pregnancy just makes everything harder!)
So I drive, most days - it takes seven minutes, instead of half an hour, each way. It means I can do shopping on the same journey, or get the 20kg sacks of pet food we use, or pieces of timber or whatever.
I tend to stay in the rest of the day and do stuff here.
Just because school begins at a busy time, that means unfortunately I help clog up the roads at that time. But I don't the rest of the time, generally.
Perhaps they ought to change school starting times instead.