Associate Transport Minister Michael Woodhouse says a new law on booster seats will reduce the number of children injured in car accidents each year.
At present, children have to be in approved car seats or booster seats until they are five years old, but this will increase to seven on 1 November this year.
Mr Woodhouse says children are particularly vulnerable in crashes as they tend to slip under seat belts, which are designed for larger bodies, and are prone to pelvic and neck injuries.
The minister says 150 six- and seven-year-olds are injured by their seatbelts every year, and the Land Transport Rule will reduce this.
The Playcentre Federation is praising the move but says the new law will provide parents with some challenges.
Its co-president Maureen Woodhams says older children may be resistant to the change and another issue may be the financial burden for some families who now have to buy new booster seats.
"Big kids need to get motivated to use car restraints, so they don't feel patronised and they feel it's an important thing they and their families can buy into."