Kennedy Kress, 7, is one of those kids that will be required to ride in a booster seat starting on Sunday.
Her father Phil says the law means more work juggling car seats, but it's safety that matters.
"We have some left in the garage so we will put them in play right after the New Year," he said.
The new restriction is a trend as California joins 30 other states with similar laws that put kids in car seats longer.
John Muir Hospital safety expert Carol Powers says children riding in a car without a proper child safety restraint could suffer organ or spinal damage in an accident.
Most retailers sell booster seats starting at $25 on up to $140 and beyond.
More than one million kids in California are impacted by the law.
Kennedy says it won't be that bad.
"I am happy, I will be able to see out the window," Kennedy said.
Violators face fines starting as $475.
