https://www.theaa.com/motoring_advice/euroncap/crash_tests.h...
http://www.howsafeisyourcar.com.au/2013/Volkswagen/Polo/Tren...
"The bumper provided mixed protection for pedestrians' legs. The front edge of the bonnet was marginal to poor. The centre of the bonnet offered good protection to a child's head but poorer protection towards the edges. In most areas likely to be struck by an adult's head, poor protection was provided."
EDIT: Seems three of us posted in the same minute. :)
But in school buses the tires are set far back from the corners, especially the rear tires. In a large bus the tires are 5-10 feet from the rear bumper. School buses also tend to have a very high ground clearance. I assume that these design features are for safety: if the bus hits a child while starting to move, either backward or forward, the driver will have a lot more time to react to the thud against the bumper before the tires reach the child. It takes a moment for the driver to notice the thud and move his foot from the gas to the brake; if the tires were at the corners that moment is all it would take for the bus to roll over the child.
So, I think this is an example where the vehicle is designed explicitly to protect pedestrians, even though it probably makes the vehicle less stable and harder to maneuver.
The other thing that moving the wheelbase in does is to make the vehicle more maneuverable overall -- it has a shorter turning radius.
Edit: And so far as I can tell, turning radius is in fact the principle concern. There are numerous versions of school bus design specs online, typical: http://ww2.mackblackwell.org/web/research/ALL_RESEARCH_PROJE...