Every child is a different shape and size, so when can they stop sitting in a car seat?
By law, Australian kids need to be in a car booster seat until the age of 7 but new research shows one in five parents keep them in there longer.
The study, commissioned by law firm Slater and Gordon, also found mums were more likely than dads to use safety restraints beyond the age of seven.
Motor vehicle accident lawyer Genevieve Henderson said car seats weren't always easy.
"Over the years, I've talked to many parents who look forward to the day their child reaches the age of seven when they can legally take them out of a seat restraint," Henderson said in a statement.
"Some say their child has outgrown any available booster seat, others say they want to free-up some space on their backseat.
"Up to 80 children are killed and thousands more injured in road crashes each year, and research shows a child in a car restraint is less likely to be harmed than one who is not."
Child restraint specialist Robert Gilbert told The Huffington Post Australia he often spoke to mothers groups and councils about the importance of keeping children in appropriate seats.
"At the end of the day it only takes a split second for something to go wrong and if the seat is not right, it could cause serious injury and even death," Gilbert said.
"You'd just never forgive yourself."
He said his company As Snug As A Bug recommended parents not switch to a forwards-facing seat until 12-18 months and to stay in some sort of restraint until at least eight years old.
Gilbert said he was a father of four and was already planning for grandchildren.
"I've already picked out which seat he or she will have."
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National Road Safety Laws for child restraints and booster seats
From birth up to the age of six months to be restrained in a rearward facing child car restraint
From six months up to the age of four years to be restrained in either a rearward or forward facing child car restraint with in-built harness.
From four years up to the age of seven years to be restrained in either a forward facing child car restraint or booster seat restrained by a correctly adjusted and fastened seat belt or child safety harness.
Children seven years and over can be restrained in an adult seat belt or in a booster seat.