Booster seats are like a combination of a glorified phone book and an advanced pelvis for your child. While most of us rode around without car seats or booster seats or even seat belts in the conversion van or in the back of a pick-up when we were kids (and we made it out just fine), we were the lucky ones. The kids who didn’t make it aren’t around to advocate for advancements in safety. Their parents had to do all the work in their honor, to which I would like to say thank you.
What a majority of caregivers don’t understand is that the seat belt in a car is designed and tested for a manikin that is 5’10” and 180lbs. Seat belts don’t fit most adult women much less an average 8 year old child.
The ambiguous cut-off for kids to be old/big enough to not sit in a booster seat is somewhere around age 8, or 4’9”, or 80lbs. In fact, most kids don’t reach 4’9” until somewhere between 9 to 12 years old, according to the CDC (boys and girls).
While your 9 year old might fit properly in say a Mini Cooper without a booster seat, they might still need one in an SUV because of the larger seats and attachment points of the seat belts.
Proper fit has much more to do with the placement of the seat belt across the child’s body, than it does with the child’s age.
In order for the seat belt to work properly, it must ride across the bone structure of the body, the shoulder and sternum (breastbone) and across the pelvis. If the seat belt slides up across the belly, in a crash, the guts squish resulting in what is commonly referred to as 'seat belt syndrome'. This can be extremely serious internal injuries. The little 'arm rests' on the booster seat acts like the tops of the pelvis in adults that will hold onto the seat belt better than a child's underdeveloped pelvis. The booster seat raises them up so that the seat belt is properly positioned across the child's body.
When we evaluate a child in a booster seat, this is what we’re looking for:
Shoulder belt fit — The shoulder belt should fit across the middle of the child's shoulder. If it falls off the shoulder or rests on your child's neck, it won't work as well. An improper fit could encourage your child to move the belt to a dangerous position, such as behind the back or under the arm.
Good shoulder fit; two poor shoulder fits
Lap belt fit — The lap belt should lie flat and on top of the thighs, not higher up on the abdomen.
Good lap fit vs. poor lap fit
Below is a series of photos of Joey two days after his 8th birthday.
He weighs 61lbs.
He is 50" or 4'2"
In the above picture, you can see the lap belt is coming up across his belly and the shoulder belt is coming across too high on the neck. In a crash, this would result in internal injuries and probably spinal injuries.
In this picture you can see where the lap belt is low across the hips and the shoulder belt is across the sternum and shoulder. The seat belt needs to cross the bone structure.
You read to your child to boost 'em at school. You play with them and cuddle to boost 'em at emotional intelligence. You get them involved in sports to boost 'em at their physical health. Make sure you boost 'em in the car until the seat belt fits properly to give them the best possible outcome in a collision.