How to choose and use a car seat
There are three basic types of car seats to choose from:
Baby (or infant-only) car seats: These should always face the rear of the car. They have a weight limit of between 22 and 35 pounds. When your baby reaches the weight or height limits for his infant seat, move him to a rear-facing convertible car seat.
Convertible (or infant-toddler) car seats: These function as both rear-facing seats for babies and toddlers and forward-facing seats for older children. Many new ones are designed to hold a child of up to 40 pounds rear-facing and up to 70 pounds forward-facing. It's safest to leave your child rear-facing as long as possible – in fact, the latest guidelines from the American Academy of Pediatrics (AAP) say to keep your child in a rear-facing car seat until the age of 2, or until he reaches the seat's maximum rear-facing height and weight limits.
Belt-positioning booster seats: These seats are for kids who are at least 4 and weigh at least 40 pounds. They use the regular car lap and shoulder belts to secure the child. Backless boosters are fine when used with an automobile seat that provides head support.