How Child Car Seats Work

Graco TurboBooster Appropriate for children from 30-100 pounds, this model comes complete with adjustable arm rests and dual slide-out cup holders.

Photo courtesy

Booster Seats


­When a child is too big for a harnessed car seat, it's time to use a booster seat. A child is to be considered "too big" if he/she exceeds the manufacturer's weight limit or the top of his/her head is higher than the top of the seat. Usually a child will need a booster seat between the ages of four and six.

We found out earlier that a seatbelt is designed to sit across the pelvis and ribcage, spreading the force of an impact over the strongest parts of our skeleton. A booster seat works by raising the child so that the adult seatbelt fits across these areas. Since the car's built-in seatbelt is being used, booster seats do not have an integral harness to hold the child in place; instead, the seatbelt holds in both the child and the seat. This means that it is extremely important to ensure the belt is correctly adjusted.

How Child Car Seats Work

Backless Graco TurboBooster

Photo courtesy NHTSA

You want to make certain that:

  • The belt is fastened securely and is as tight as possible.
  • The belt should go over the pelvic region, not the stomach.
  • The diagonal strap should rest over the shoulder, not the neck.

Usually by the age of six, or when a child can sit up straight on their own, without slumping or slouching, he/she can graduate from a full booster seat to a backless booster seat. A backless booster seat is simply a standard booster seat without the backrest. As with other car seats, you can find convertible booster seats that transition from a backrest-inclusive model to backless. It's important to remember that, when sitting in a backless booster seat, your child should sit up straight so that the diagonal strap of the seatbelt rests on your child's shoulder and not across his/her neck.

How Child Car Seats Work

Dorel/Cosco AutoBooster

Photo courtesy NHTSA

A child is not ready to use a regular seat belt until:

  • He/she is tall enough so that his/her legs bend at the knees against the edge of the seat.
  • He/she is mature enough to remain seated with his/her back flat on the seat, not slouching.
  • The lap belt sits high on the thighs or low on the hips, not on the stomach.
  • The shoulder belt crosses the shoulder and chest, avoiding the arms and the neck.

A child ready to use an adult seat belt without the aid of a booster seat will be around 4 feet, 9 inches (about 1 1/2 meters) tall and roughly eight years old. Please keep in mind that, because children do vary in size by age, some children could still need a booster seat at the age of 10 or 11.