I will only add the most school buses do not have seat belts. So if the truck had hit the bus at full speed, you would have ended up with many more dead than the 7. And most likely there would have been many serious injuries including being parilized. The kids would have hit the roof or rolled down the center row.
No matter how you look at this, it was a terrible accident. People would have been killed either way. If an adult was driving, then only maybe 5 would be dead, at this point it really does not matter.