Think by kindergarten your child should be free of all car seats? Think again.

When a child is ready to transition out of a booster seat has less to do with age than it does with height and weight, according to the American Academy of Pediatrics (AAP).

The AAP says children who have graduated from a forward-facing harness seat should remain in a booster seat until they are between 80 to 100 pounds or, more important, at least 4 feet 9 inches tall. Around that height, the lap part of the belt fits snug on the child’s thigh and the shoulder strap fits across the shoulder and over the chest.

That means it may no longer be uncommon — and is totally appropriate — for kids up to 12 years old to ride in booster seats, says Gina Duchossois, an injury prevention supervisor at The Children's Hospital of Philadelphia and chairwoman of Safe Kids Southeastern Pennsylvania.

However, a survey by Safe Kids Worldwide of 1,000 parents found that 70 percent of parents did not know the height limit for booster seats, and an estimated 90 percent of parents graduated their child to a vehicle seat too soon.

Forty-nine states have laws requiring booster seats, according to the Governors Highway Safety Association. “Having a law raises the awareness of not only putting your child in a restraint, but the type as well,” Duchossois said.

While it’s important to know your state’s law regarding safety seats and booster seats, a law may not be enough to know what’s right for each particular child. That’s because booster seats are not one size — or age — fits all.

Two types of booster seats provide different types of coverage. The high-back booster seat should be used in cars that don’t provide head and neck support. Backless booster seats can be used in larger back seats that have head rests, according to Duchossois.

Commercial booster seats — whether it’s a high-back booster seat or a backless seat — list height and weight limits that offer the easiest indication of when it’s time to move on.

“I think parents want to do the right thing, and they don’t want to graduate their kids too early,” said Duchossois.

Kids often provide hints that they’re not ready to move out of a booster seat into a regular vehicle seat, Duchossois said. One way to tell is to have them sit in the car without the booster seat, buckle their seat belt and see how they react.

“The child may possibly put [the chest strap] behind the arm,” Duchossois said. “If they do that, they may not be ready.”

They may also tug at the chest strap because it is irritating their neck. That indicates they are still too short to sit in a regular vehicle seat.

“You want to make sure he can sit upright with the back against the seat and his legs coming over the seat and can stay in this position,” she said.

Car crashes are the second leading cause of death for children between ages 4 and 10, according to Safe Kids Worldwide. One-third of the deaths may have been prevented if the child was properly restrained.

This is why “we don’t want to rush to graduate children to the next seat,” said Duchossois.

Lara Salahi is a multimedia journalist who specializes in health and medical news.