Older children are placed prematurely into booster seats or even straight into adult belt systems. The next most common error involves not fitting the restraints correctly to the vehicle. Seats differ substantially, model to model, in how they are fitted. Because some seats are not well suited to certain vehicles, it's wise to try the seat in your own car before buying. The seat must be firmly strapped down.
Some seats require a clip to be placed on the car's seat belt.
These instructions always specify what size child the seat suits and depict just how to fit it. There may be a marked path for the seat-belt straps. Following all instructions carefully is vital. The child must be strapped in correctly. In principle, the tighter the straps the better, but in the real world some compromise will be necessary.