The laws require all children up to the age of seven to be restrained in approved seats.

Warrnambool mother Karen Benson said she did not know how most parents, particularly those with smaller cars, would be able to fit three child seats in.

Mrs Benson, who drives a Subaru Outback, has two young children and would like another.

"I don't know how we would fit another seat in. We look at some cars and think there's no way they would fit," she said.

The confusion also came as Warrnambool's child restraint fitting station this week confirmed there were no booster seats on the market that catered for older children.

"A lot of people are asking questions and at this stage, there are no answers," Ian Warner from fitting station South Coast Auto Services said.

Mr Warner said many children now stopped using restraints at about five years of age when they went to school and their parents believed they were not necessary any more.

"All booster seats that we are aware of are rated to a (weight) maximum of 26 kilograms," Mr Warner said. "I haven't found any booster seats that cater above that."

He said manufacturers were being urged to supply a seat that was capable of taking up to 32 kilograms.

"I reckon there will be a lot of kids near the seven-year age that are in that upper (weight) range," he said.

He agreed that families with several young children would also face problems trying to fit three baby or booster seats in the back of their vehicles.

Smaller cars would not take three seats and parents with larger cars would still find it difficult to connect the seat belt buckles between the seats.

Mr Warner said the manufacturers were reported to be looking at solving this problem by placing a cut-out near the base of the restraint to allow better access to the seat belts.

However, he expected the new model seats would not be available for at least 18 months to two years.

VicRoads spokeswoman Sarah Kulman said the new laws aimed to cater for the majority of children.

"As with all road rule changes, Victoria Police trains its members on what to look for when enforcing particular rules.

"If someone has followed these rules correctly and they feel they have unfairly received an infringement, there are avenues for them to contest that infringement."