One of the most important things to remember about child safety seats is proper fit. If a child is too big ot too small for a seat, it will not protect them effectively. The most effective aspect to consider when choosing the correct safety seat is a child's weight. Ages are just approximate guidelines.
Here are some guidelines for sizing child safety seats:
Infants should ride in a rear-facing or convertible safety seat in the rear-facing position until they are 1 year old AND weigh 20 pounds. If the child is less than 1 year but weighs more than 20 pounds, the child should be placed in a rear-facing convertible safety seat. Harness straps on these types of seats should be positioned at or slightly below the child's shoulders with the harness chest clip at armpit level. The straps should be snug and straight. The seat should sit at a 45-degree incline.
From 20 pounds to 40 pounds (usually from ages 1 to 4), children should be placed in a forward-facing safety seat. The harness straps should still be at shoulder level or slightly lower, with the straps straight and snug. The chest clips should still be positioned at armpit level.
From 40 pounds to 80 pounds (approximately ages 4 to 8), children should ride in booster seats that help seat belts fit correctly. Booster seats need to be used with lap and shoulder belts for proper safety. Booster seats should always be used with lap and shoulder belts in a vehicle. Lap belt-only seat belts should NOT be used with booster seats.
Children over 80 pounds are usually big enough to fit standard lap and shoulder belts correctly. For the best fit, the child also should be at least 4-feet 9-inches tall. The shoulder strap should fit over the shoulder, but not touch the neck, while the lap belt should fit low on the hips and not over the stomach.
Whenever possible, children should ride in the backseat of the vehicle.