Are 5-point harness car seats really necessary once my child is over 40lbs?

Yes! Ordinary booster seats require that their 5 point harness be removed at 40lbs and restraining your child using the seat belt. This leaves your child at the mercy of the seat belt not failing. But as Kyle's death has taught us, we know that seat belts do fail, more often than is reported. If your 5-point harness car seat is secured using a seat belt and this fails during an accident, and your child happens to be ejected from the car, the child is cocooned within the car seat and secured with the harness, which will potentially result in fewer injuries. Furthermore, children who are secured in an ordinary booster with a seat belt for restraint often unbuckle the seat belt, put it behind their shoulders, or sit awkwardly in the seat - not in a position that was crash-tested. The only way to make sure you child is properly secured 100% of the time, is to have them in a 5 point harness.