A doctor at Starship children's hospital says an increase in the age up to which approved child restraints must be used in cars is not enough.
From Friday, all children must be fastened into child restraints until age seven, two years older than previously required.
Intensive care doctor Elizabeth Segedin says children are up to three times less likely to be seriously injured in a crash if they are using a booster seat, compared with using a standard seatbelt without any special seat.
Dr Segeden says the height required for children to wear a standard seatbelt is between 145cm and 150cm, which most children will not reach until between the ages of nine and 12.
She says the age for mandatory child restraints should therefore be raised to at least ten.
Baby and child welfare group Plunket agrees, although national child safety adviser Sue Campbell acknowledges there is some resistance to the new rules.
The Government says increasing the age to seven aligns New Zealand with the rules in Australia and Japan.
Associate Transport Minister Michael Woodhouse says the change will reduce the number of children injured in car accidents each year.