Measuring a child to check compliance with a height-based child restraint law would be ''ridiculous'', Dunedin police road policing manager Senior Sergeant Phil McDouall said.
But a child safety advocacy groups say a height-based rule would be better than the incoming age-based restriction.
From tomorrow, the mandatory use of child restraints in vehicles will be extended by two years. All children will be required to be correctly secured in an approved restraint until their 7th birthday.
Snr Sgt McDouall said police would not remove children from vehicles if a height-based rule was brought in as part of the child-restraint legislation.
''We wouldn't be that ridiculous to take somebody out of a car seat to measure them.''
Children would be asked their age to check compliance with the new age-based rule.
''A 7-year-old will know they are 7,'' Snr Sgt McDouall said.
If a child was unaware of their age, their caregivers would be asked to provide their age.
''And if [say] they don't know, they are probably lying to us.''
Police would be randomly checking the child restraints in Dunedin over two weekends next month.
Non-compliant caregivers would be warned, he said.
Safekids Aotearoa director Ann Weaver said Safekids Aotearoa had campaigned for a height-based rule of 148cm since 2009.
The campaign was supported by both Plunket and the Automobile Association.
''Unfortunately, the Government had decided to go with age-based and aligned with Australia.''
Seatbelts fitted people who were 148cm and taller and Safekids Aotearoa estimated that half of New Zealand children still should use a booster seat at the age of 10. Children in a vehicle crash could receive severe head, spine and abdominal injuries when using seatbelts that were too big for their size, she said.
''While we are pleased the Government has taken a step in the right direction, we still want it to go further and look at it from a height perspective, rather than an age perspective.''
There were easy ways to police a height-based rule, she said.
''We know the height of a police car is 148cm - there are ways of measuring children.''
Safekids Aotearoa is a service of Starship Children's Health, established by Starship Children's Health Trauma Service to help reduce the high rates of preventable injury to children.
