Car booster seats should be used for children from approximately age 5 and up until the child outgrows it and is big enough for seatbelts to fit properly. Car booster seats are front-facing, and children using them should only ride in the back seat.
Children small enough to require a booster seat are also small enough that air bag deployment can severely injure or kill them, so they should always ride in the back. Ideally, they should also be positioned in the center of the back seat if possible as it is the safest location. Some guidelines state that children should be at least 4 feet 9 inches tall and be between 8 and 12 years old before they stop using booster seats.
The exact age that a child moves from using a car seat to a booster seat varies depending on the size of the child. Refer to manufacturer's guidelines when deciding when to make the change. The age that a child graduates from the booster seat to just using a seatbelt varies even more depending on the child's size and the type of car. The lap belt should rest on the child's upper thighs, and the shoulder belt should cross the chest when the booster seat is removed. If the lap belt crosses the stomach or the shoulder belt crosses the neck, the child is too small and still needs a booster seat.