At what point should the seatbelt be the sole restraint for a child?

The point at which a seatbelt can be the sole restraint for a child is when they can sit properly against the seat. This means the child is able to sit all the way back against the vehicle seat with their back straight and their knees naturally bending over the edge of the seat without slouching. Proper positioning is crucial; it ensures that the seatbelt fits correctly across the stronger parts of the body—specifically, the shoulder and across the lap—rather than across the neck or stomach, which can lead to injury in a crash.

It's important to note that age, weight, and height alone do not determine when a child is safe to transition from a booster seat to just using a seatbelt. Children come in different shapes and sizes, and proper fit is the key factor in ensuring their safety during travel.