Now, a lot comes into play here - the bus outweighs the pickup by several times, so it has the momentum to absorb the oncoming momentum and keep moving. But it's certainly not like hitting a flying bug. All that energy from the truck headed the opposite direction has to go somewhere, and it slows the bus dramatically in an instant. And these are high schoolers - no matter how many times the driver reminds them to sit down, sit correctly, they just won't. And even after all that, with no one besides the driver in a seatbelt, the students were all OK. (To satisfy curiosity: the driver of the pickup took serious injuries of which none were life-threatening; he spent two days in the hospital. He'd gotten impatient driving behind a tractor/trailer and decided to pass immediately after a curve without checking the lane first. This was a two-lane state "highway" and he was indeed in a zone that allowed passing.)

Then there's the Really Bad Accidents where the bus ends up on its side or upside down. Seatbelts are designed the hold under stress-- the button becomes near-impossible to operate and release. Smaller children will require the assistance of an adult. And there's ONE on the bus. With 50 kids. They make a safe belt cutter that a driver can carry, but now the driver has to visit every seat with multiple belts, cutting kids free, supporting them so they don't fall. This is not a scenario I'd care to have enter reality.