(The vehicle and the safety seat each have weight limits set by their manufacturers.
Most children will not fit seat belts without a booster seat until 10 or 11 years of age. Children are large enough to use the vehicle seat belt typically when they reach 4'9" tall and are between 8 and 12 years of age.Find a car seat with harness that will fit his/her height and weight. If your child climbs out of the booster seat or will not sit upright for an entire trip, it is not safe and too soon to switch. Booster seats must be used with a lap AND shoulder belt. A belt-positioning booster seat is used until the vehicle's lap-and-should seat belt fits properly. Booster seats are for older children who have outgrown the forward-facing car seat (check car seat's height or weight or shoulder height limits).Keep child in car seat with harness until they reach the harness height limits, or the maximum weight or height allowed by the manufacturer of the car seat. Children should use a forward-facing car seat with a harness for as long as possible. Children should use a forward-facing car seat with a harness when they have outgrown the rear-facing seat (check maximums of car seat's rear-facing height or weight).Rear-facing is the safest seat position for children and many car seats can rear-face a child up to 40 or 50 pounds. All infants and toddlers should ride rear-facing as long as possible, until they reach the highest weight or height allowed by the manufacturer of the car seat. All infants ride in rear-facing car seats starting with their first ride home from the hospital.Keep your child in the current seat and positioning for as long as possible (according to the seat manufacturer's height and weight requirements), to maximize safety.
Get the best safety benefits of your child’s car seat by following these recommendations, provided by the American Academy of Pediatrics. Car seat and booster seat recommendations