If the belt fits low and tight across the top of the user's thighs the child should be able to sit comfortably and safely. The correct position to seat in the car is with ones buttocks against the seat back during the entire ride. Slouching, which can happen with children, does not allow the seat belt to fit properly. A shoulder belt is another seat belt that you might consider putting your child in after a booster chair. If you decide to do this make sure that the belt goes across the shoulder, not the throat or face.
Injuries can happen if the shoulder belt is too high.
Choosing a booster depends on which type of belt you have in your car. A shield booster is intended for use of a lap belt. It is less effective as a child gets taller. To ensure the best possible safety use a locking clip to restrain the lap belt around the shield or through the base of the shield booster. The BPB provides better protection than the shield booster because the shoulder belt reduces the distance that the child's head can move in a crash-and limits what it could hit.