California is the latest state to tell 6 and 7-year-olds to get back into their car seats.
A new measure that kicks in Jan. 1 will mandate car seats for children until they are 8, or 4 feet 9 inches tall. Under current law in the state, kids must be in car seats until they are 6 or 60 pounds.
The measure—signed by Gov. Jerry Brown after similar bills were previously vetoed twice by former Gov. Arnold Schwarzenegger—moves closer to guidelines from the National Highway Traffic Safety Administration.
The penalty for violating the new law will be a minimum of $479 for a first offense, according to a spokesman for the California Office of Traffic Safety.
The NHTSA recommends booster seats for 8 to 12-year-olds, or until the child can fit properly into a regular seat belt, with the lap belt across the upper thighs, not the stomach, and the shoulder belt across the chest, not the neck.
The American Academy of Pediatrics also recommends a booster until the seat belt fits as it should—usually between ages 8 and 12.
States that now mandate car seats up to age 8 include Maine, Maryland, New Jersey, Texas and Washington.
Kristy Arbogast, engineering director at the Center for Injury Research and Prevention at the Children's Hospital of Philadelphia, said 8 is the earliest that a child should give up a booster seat.
"We really have no doubt this was the right thing to do," she said, citing research at Children's Hospital in 2009 that showed a 45 percent reduction in risk when children were in booster seats between the ages of 4 and 8.
"It's all about seat-belt fit," said Arbogast. When the belt hits the neck, she said, kids will often slip out of the shoulder belt and put it behind their back—leaving them at risk of skull fractures and brain injuries in a crash.
As a parent, she sympathizes with California moms and dads who will have to tell their 6 and 7-year-olds to start sitting in a booster seat. "It's going to be tough," she said, but suggested parents should tell kids: "It's not mommy and daddy's decision, it's the law, it's the police."
A good technique, she said, is to keep younger children in high-back booster seats as long as possible, then transition to backless boosters for older kids. They have a big plus from kids' point of view: you can't tell from outside the car that the child's sitting in a booster seat.