In the United States, car-seat laws vary from state to state. The general rule is that children 5 and younger must be in a car seat, and many states require that children be restrained in a booster seat until they reach age 7. Safety experts recommend that car seats be located in the rear seats of vehicles, away from airbags. Three common types of car seats, produced by a variety of manufacturers, can be secured with a lap seat belt only.
Infant-Only Car Seats
Infant-only car seats are generally used for children who weigh up to 9.98 Kilogram. These seats are rear-facing and attach to a base that is secured in the back seat of the vehicle with a lap belt, lap belt/shoulder belt combination or LATCH system. A useful feature of infant-only car seats is the infant carrier, which can often be placed in a stroller and does not require the child be removed from the seat. The weight limits vary from model to model. Once a child reaches the limit, she must be transitioned to a different type of seat.
Convertible Car Seats
Convertible car seats can be positioned as rear-facing or forward-facing. These seats do not attach to a base. They consist of one piece that is secured by the same means as an infant seat: with the lap belt, lap belt/shoulder belt combination or LATCH system. Convertible car seats can be used for infants as well as older children because of the ability to face forward or to the rear. The child weight limits for these types of seats vary among manufacturers.
Forward-Facing Car Seats
Children are typically required to be in a rear-facing car seat until they reach 9.07 Kilogram and are at least a year old. After that, a forward-facing car seat can be used. These seats are built to face forward only and can attach to the seat with the lap belt, lap belt/shoulder belt combination or LATCH system. Forward-facing car seats often convert to booster seats by removing the harness and using the lap and shoulder belt in the car. For cars without a shoulder belt, this type of seat is useful because it properly restrains a larger child who otherwise would be in a more traditional booster seat.
Lap Belt Precautions
When securing a car seat with a lap belt only, be sure the car is equipped either with seat belts that have an auto locking feature, meaning that once they are pulled taut they stay in place until they are released, or belts that use locking clips to keep the belt in place. Many newer car seats come with locking clips already installed. Booster seats cannot be used with lap belts only; they must have the shoulder belt to work properly.