My son received a contact card from the bus driver on the first day, and a tag on his school bad indicating the bus name, number and his pick up and drop off location.
The school bus always has at least one helper on board.I think it's her who answers calls from parents.
When dropping off, the bus never leaves scene before the student enters home or picked up by an authrized person.
In my case, PTA recommended this school bus, but they don't really handle anything more than that.
Lesson learned here is to know how school bus works in your area and know what to do if this happens again. After all, leaving kids on the street doesn't seem to be a right thing, but again it's not really your legal resposiblity either.