There is no such thing as a double car seat, although there are adapters which fit two separate infant styled car seats so that they can both fit in a double stroller. A double car seat would not be able to fit snugly and safely enough in most cars in order to ensure the safety of a child. It is recommended that each infant under the age of one and 20 pounds (9.1 kg) be secured in a car seat designed for young infants, and that the seat be installed rear-facing for as long as possible.
Car seats are designed to support the head, neck, and back of an infant or young child so that he or she has a greater chance of survival in the event of a crash. Most seats have various settings to accommodate the child as he or she grows. All seats also have height and weight limits, so parents should be sure to switch to a larger model seat when their child outgrows his or her current seat. Since many car seats are not installed safely, it is recommended that parents seek advice from a trained professional to ensure that their seat is being used properly.
Although the concept of a double car seat sounds convenient for parents who have twins or more than one young child, it is not feasible to have this sort of device in most cases. Seats have to be strapped into the car using either the safety belt or latching system. Each belt is designed for only one passenger per seat. A side-by-side model would not work much better because the seats would need to be perfectly aligned on their respective seats, and since all cars' seats are different sizes, matching a car seat perfectly in this way would be nearly impossible.
Options are available for parents who want to use a double car seat. There are dual strollers which are designed to hold two or more children at once. Adapters are sold to fit more than one carrier styled infant seat so that both can be carried in one unit. Some strollers are also made to hold more than one infant seat. Car seats have to be removed from these adapters before being placed in the car.
Most car seats are generally about equal when it comes to safety requirements. They are all tested and held to the same stringent testing procedures to ensure that they meet or exceed all government-mandated safety requirements. In some cases a particular seat may not be a good fit for all children. For instance, some seats are slightly larger or smaller than others, so very small infants or premature infants may not fit appropriately. It is important to follow all manufacturers' instructions when installing and using an infant seat.