Booster or Harness for big kids?

So the law of NZ tells us that after 7-8 years old legally our children no longer need to be in a child restraint or car seat. 

Safety wise - we know this is not the case. Children are not usually physically ready to use just an adult seat belt until they are around 12 years old, or 148cm. 

This is where parents get it wrong sometimes - and where NZ get it wrong in a big way. We have limited education available for parents to support them in making informed choices in regards to car safety. 

While this video is aged in terms of crash videos - it shows very simply the difference of a child that is in a booster vs a child that is in a 5-point harness belt. As a Child Restraint Technician I will always endorse best practice, and best practice is now found that extended harnessing is safest for children when they still meet the limits of the child restraint. 

For me, as a Mum, it is fool proof evidence. Keep them harnessed as long as you can to ensure they have the best chance in the worst moment, an accident. 


So when are they ready for a booster? 
This is not a simple answer - each child is different. The general guideline is as below:

  • Can they sit still most of the time and not wriggle around around when sitting in their seat? 
  • Have they outgrown the harness limit of their harnessed seat?
  • Are they at least 5 years of age?
  • When sitting in their booster does the seat belt sit across the shoulder? And high on the thighs? We do not want the seat belt sitting across the stomach or close to the neck.
  • Do they meet the minimum requirements for the booster you are planning on using?

Another blog will come that compares full boosters and half boosters. However - use a full booster for as long as possible. This provides side-impact protection to the head and ensures a well positioned seat belt. Half boosters are for bigger kids that have outgrown the full-back booster

If you need to look into a booster for your big kid to keep them safe while travelling then check out the options we have available as well. And ask questions as you need to! 

When are they ready for an adult seat-belt?

The next stage is when is my child ready to just use an adult seat belt? The law says between 7-8 years old in NZ. However, safety research says when they are 148cm. Children are not normally ready for a full seat belt until they are around 10-12 years old. 

The 5-step test is one that is internationally used to see if children are ready for a seat belt yet.  

If a child passes the 5-step test then they are able to use an adult seat-belt. Beware however - the way they sit will change in each position in the vehicle, and between different vehicles. So always check before travel! 

Image taken from The Car Seat Lady


There is lots of videos and research out there that shows the benefit to extended harnessing. Some other awesome articles can be found at:

The Car Seat Blog

Car Seats for the Littles


As always - if you are unsure ask a Child Restraint Technician for support or contact us for information! 


Nicky Creevey

Nicky Creevey said:

Thanks Claire! This exactly answers my questions about putting Mr 6 into a booster or keeping him in the 5point!!
Great post ;-)

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