Why make such a big deal about something that may appear to be so minor, so trivial as how someone's kids may or may not make their way to school? Well, if they're yours and this is something that you have to think about and act on every day (and perhaps not always quite as well as you might like), you already have some developed thoughts on this. But for the less initiated, by way of quick intro and first reminder, it may be useful to quote that reasons that the California Department of Health Services cites for its involvement in this area:

As you will see as you look through the abundant materials assembled here there are many more reasons than that, but their public health perspective gets us off to a great start.