Contact your local police department about getting a car seat check-up. Next year, California will require that children up to six years and 60 pounds be placed in booster seats. These allow seat belts to fit properly across children's hips and chests. Children should use booster seats until they can sit with their knees bent at the edge of the seat and their backs comfortably against the seat back. A seat belt fits properly when the lap belt crosses the hips, not the stomach, and the shoulder belt crosses the chest, not the face or neck.
Many websites contain excellent auto safety information.
2223 in Northern California.