I’ve gone to a bus stop in -40° weather before (northern Alaska), frostbite isn’t that much of a concern if you have good enough clothing (children should not be sent out in fabrics that lose all insulating properties when wet spend the extra if they are going out in even -20°C regularly) handwarmers do exist for gloves if the child has learned how not to burn themselves (and when burns are preferable to freezing) and they get their gloves wet.

it would be nice if school buses had trackers so kids could know how delayed they currently are (or if the route is canceled because the bus drove off the road again).