Do seat belts kill?
If worn incorrectly (tucked under armpit for example) and a collision happens then yes you can die even wearing a seatbelt. The belt can press into a person's stomach hard enough to do damage (compressed lungs, burst intestines, pressure damage in general).
Even worn properly people can regularly get cracked ribs in car accidents, however this is significantly less damage than would be incurred if you were thrown out of the car window as a result of not wearing a seatbelt in a collision.
Seat belts can possibly decapitate you. As such can occur if a crash is violent enough. Luckily, most are not.
Some school buses do have seat belts throughout the entire bus. For the most part, buses do not have seat belts. They tend to have seat belts in the rows closest to the front end. It depends on the town, village, city, that owns the buses. Some places make them regulation to have entire buses full of seat belts, while some don't have any. Bus drivers usually have seat belts, being drivers.
Side impact crashes, immersions in water where the victims cannot undo their seat belts and drown, rollovers where the victims are crushed, fires where the victims cannot get out and are burned to death, and other high speed crashes where the victims suffer extensive intestinal and other internal injuries directly caused by the seat belts that kill them. Non-use often causes surface injuries, including broken bones that will heal in a few weeks, but certainly…
Children up to certain weights are required to be in car seats that are held in place with the seat belts in most states. After they reach a certain weight, they are required to wear seat belts, so not only can children wear seat belts, after they no longer are required to be in car seats, they are required to wear a seat belt.