Children should be strapped into car seats until they are at least 11 years old or 5ft tall, ministers have said.
35 children aged up to 11 were killed in 2002 while travelling by car
Research by the THINK! road safety campaign found that 63% of parents abandon using safety seats by the time their child is six.
One in 10 parents stop using car seats by their child's third birthday and 26% said their 11-year-olds use a seat.
Minister David Jamieson said: "Child restraints play a very important part in keeping children safe inside cars."
The THINK! campaign says using child car seats or booster cushions until youngsters are at least 11 or 5ft tall reduces the risk of injury in the event of an accident and is the best way to protect them when travelling by car.
In 2002, 35 children aged up to 11 were killed and 480 seriously injured when travelling in cars.
It is illegal for youngsters under three to sit in the front unless they are strapped in to a proper child car seat, or for older children to sit in the front seat without using a seatbelt or safety seat.
To spread its message, THINK! is launching an advertising campaign to encourage parents to keep their children in car seats up to 11.
Road Safety Minister David Jamieson said it was "vital" child restraints were fitted correctly and "they continue to be used for as long as is necessary".
"I hope this useful advice we are issuing today encourages parents and guardians that double-checking their use of car seats can improve their child's safety," he said.
Marianne Le Claire, head of child safety research at the Transport Research Laboratory, said : "Children travelling in cars need to be in a purpose built child car seat or booster until they are either 11 years old or 150cm tall.
"Adult seatbelts will not fit them properly and will put them at higher risk of injury, in particular to the chest, lungs, abdomen and spine, in comparison to a purpose built child seat.
"However, if there is no alternative, restraint with the adult belt is better than no restraint at all.
"Parents can help reduce this risk by taking the time to fit a child car seat or booster seat correctly and making sure their child uses it on every trip."
The THINK! campaign's top safety tips for parents include:
Ensuring child car seat harnesses are properly adjusted and fastened before setting off in the car, even for short trips.
Fastening your own belt as a good example.
Using a properly fitted, purpose built child car seat which meets current safety standards (marked with an 'E' and an '03') and is appropriate to a child's weight and height.
Get a trained shop assistant to demonstrate how to fit the seat.
Check second-hand child car seats meet current safety standards, have not already been in an accident and have correct fitting instructions.
Never use a rear-facing child car seat in a seat protected by an active frontal airbag. Forward-facing child car seats should be as far back from the airbag as possible. Check the car handbook for manufacturer's advice.