Give me a Boost! When to use a booster

I’ve been putting this article off for months, it’s been asked for many times. Yet I kept delaying because, of all the topics I’ve touched on in car seat safety, few are as contentious and fought by parents as when kids should use a booster seat. Both when to start and when to stop. People give a million reasons why they can’t use one or why it’s ok to use one too soon “The law says it’s ok” being the most common. But really some things are important and worth talking about, and safe booster use is absolutely one of them, so here we go.
So when can I use a booster?
Well first off let’s start by explaining terminology since the term booster is in and of itself convoluted. There are 3 types of boosters:
Harnessed Boosters – generally you will see these with a 6 month to 8 years label on them. They are seats that have a fully integrated 6 point harness (just like a regular car seat) that comes between the kid’s legs and over both shoulders. Some of these later turn into Belted Boosters and some do not.
Belted Booster with a high back: is a booster that has an inbuilt back support and head rest but no longer uses a built in harness and instead relies on the car’s seat belt to keep your child in place.
Belted Booster, backless: sometimes called “bum boosters” these seats don’t have a back or head rest, they are no longer sold new in Australia but can still be bought used, hence why I included them.
So back to the original question, when can my kid use a booster?
If it’s a harnessed booster, as early as 6 months provided your child meets the height entry markers for that particular seat. But safely, kids are best kept rear facing as long as possible for a couple reasons.

Their bodies are grossly disproportionate until age 2 with most of their weight in their heads.
The bones in their spinal vertebra don’t fully ossify until closer to age 4.

Both of these put them at a much higher risk of serious neck and shoulder injuries, including internal decapitation. Meaning, you want to keep them rear facing for AT LEAST 2 years if possible and ideally as close to 4 as you can get. So just because you CAN put a 6 month old into a front facing harnessed booster doesn’t mean you SHOULD.
If it’s a belted booster (high backed or backless) the legal (bare minimum) the answer is 4 years old. However here’s why you shouldn’t at 4.
Most kids quite simply aren’t ready for the responsibly of a belted booster. A belted booster uses an adult sized seat belt across a kid sized body. It puts tremendous pressure on a very small area of the body, pressure that not fully ossified bones may not handle as well as adult ones. Most experts agree that the sheer force exerted over that small area is dangerous to a child this age even WITH a booster used 100% properly. And here’s the kicker, kids that age RARELY use them properly.
They move, they wiggle, they bend over to get a toy or a sibling, or to get your attention. They slouch, they tuck belts behind themselves, they loosen them up because they are too tight, or they fall asleep and out of position. All of those things cause two problems.

They introduce a potentially dangerous amount of slack into the belt system
They move the belts out of alignment with the pelvis and sternum and over far more vulnerable areas like their stomach and throat.

Meaning, in an accident that belt that was supposed to protect them now becomes deadly. Kids die of internal injuries and head injuries a lot when using belted boosters. Not because the seats are innately unsafe but because they are kids, and they are too young to handle the responsibility of using them correctly every time. Very few kids under the age of 5 1/2 or 6 1/2 will honestly use them right.
We went on a short trip when DD was about 4 and tried to use a belted booster for a 30 minute car ride and it was seriously the most miserable experience ever. Constantly having to tell her “sit up straight, no you can’t lean over, no you can’t do that” was really draining for all of us. I realised then how true that age concern was. We tried again at 5, still not ready, and again at 6 when I could finally see the responsibility of it click for her.
Even now at 6 1/2 she’s still in a harnessed booster because at the end of the day I know it just allows less likelihood of her being out of position in an accident and because it spreads those crash forces over a wider area than a standard belt. For now she fits in her harnessed booster so there’s no reason to rush out of it. Yes, she’s one of the last kids in her first grade class using one. But you know what? I don’t care. She’s safer. And I’ll happily explain that to any parent or kid who asks. She’s not embarrassed. She understands cars are dangerous and that accidents happen, she knows why she’s in one and is ok with it. And even if she wasn’t honestly, I’m her mom and it’s my job to sometimes say sorry sweetie our rules are X even if everyone else is doing Y.
A great thing recently within the past year, is a whole new category of seats came out called Type G’s, that are strictly harnessed boosters that last most kids to 8+. That means they can stay safely harnessed for longer without being rushed to the next stage because they’ve outgrown the harness.
Ok so we know when they can go into a belted booster (between 5 1/2 and 6 for most kids, when they can be responsible and follow the rules every time), but when can they STOP using one?
Legally the answer is 7 in Australia. But once again ‘legal’ doesn’t mean it’s right – it means the BARE Minimum. When else as parents do we do that? Safely the answer is VERY different. To leave a booster a kid should meet what is called the 5 step test.
So what’s a 5 Step Test and why don’t we talk about it more?
The 5 step Test is when your kid can do ALL of the following for the whole car ride (no 3 out of 5 isn’t good enough 😉
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As the graphic above shows most kids are between 10 and 12 when they can meet ALL of those rules. For most that means they need to have reached a height of about 145 cm tall, for some a bit more depending on leg and torso height. You might have an exceptionally tall 8 year old who hits all those marks but for the most part it’s few and far between. Meaning kids who are 7, 8 or 9 really have no business being out of a booster in a car.
And yes I get that the average 9 year old may not be keen on using a booster but honestly are they keen on eating healthy, doing homework, turning off the TV or brushing teeth? And if they aren’t does it stop us from saying they have to anyway? Why only for car seats are we not willing to fight that fight? For something that could literally save their lives? Because taking away that booster too soon means that once again that adult sized seat belt is being used incorrectly and unsafely. In an accident it can kill them through internal organ damage or neck injuries.
People like to say “But I’m an adult and I can’t even meet those guidelines and I don’t use a booster” to justify not using one. But the problem is you as an adult have a different body composition than a kid of 8 or 10. Kids don’t fully ossify (harden) their bones til about 13 meaning that until then, without a booster they are much more vulnerable to internal injuries from an under ossified pelvis or other bones. Simply said, they can’t withstand safely the same forces you and I can even if we don’t fully meet those guidelines.
Lastly, I’d like to address bum boosters (backless boosters). The reason they are no longer manufactured in Australia is that they don’t meet the requirements for side impact protection. They really aren’t a good choice at all for kids under 7 since they can lead to more kids sitting out of position than even a normal high backed booster. However, if your kid is just too big for the high back boosters on the market then yes pick one up second hand to make sure to try and kepe them as safe as possible until they can meet that 5 step test above. Otherwise stick with a seat that offers the best possible protection in an accident.
I know there’s a lot of info here to digest and much of it is contrary to the norms we see everyday at school drop off and in our social groups, but we need to lead by example as parents and show our kids that just because the rest of the crowd does something it doesn’t make it the right or safe thing to do. Know better, do better as always.