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5 Things I Didn’t Know About Booster Seats

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Before I took my Child Passenger Safety Technician (CPST) training through the Child Passenger Safety Association of Canada, I didn’t know a heck of a lot about booster seats. My oldest is four-and-a-half years old and meets the weight and height minimums for a booster seat, so I considered getting one for him to use at my parents’ place in BC when we visit, ostensibly because it would be “easier.” I’m so glad I talked to a friend and fellow CPST about this because she helped me understand that booster readiness is not just about height and weight: maturity is a very important factor. In the end, we brought a lighter weight car seat with us to use for my son.

In the booster seat section of my CPST course, I learned even more things about booster seats that made me very grateful I hadn’t decided to order a random booster online and have it shipped to my parents’ place.

Cub will be harnessed at least through kindergarten, but he will eventually transition to a booster. Now I feel like I am well-equipped with knowledge and resources to make the best choice for him and for our vehicle, and I want to share what I learned with you!

5 Things I Didn’t Know About Booster Seats

1-Children are not ready for a booster seat until they’re between five and seven years old.

I had the “milestone” weight of 18 kg (40 lbs) in mind when I thought about transitioning Cub to a booster seat, but that’s about all I had in mind. Cub is over 18 kg, which means I could put him in a booster seat. And there are children much younger than Cub who are also technically big enough for a booster seat, but it’s not just a child’s physical size that is so important.

(Note this is an American graphic, thus the 30-lb limit.)


—>Maturity matters for booster seats <—

Think about who’s “in charge” when your toddler or preschooler is in their harnessed seat. They might be able to climb into their seat themselves, but most kids cannot buckle themselves in. Once they’re buckled properly, only some very MacGyver-like kiddos can manage to escape their harness. When they drop their granola bar or stuffed animal, they’re pestering you to turn around and contort your arm to reach it and pass it back to them. When it’s time to get out of the car, they’ve got to wait for you to let them out. When they fall asleep, their head might tilt forward or to the side (and head slump isn’t a concern unless we’re talking newborn babies), but their body will remain upright thanks to their harness.

Children in booster seats are in charge of their own safety. Even if you buckle them in and you ensure that the seat belt is sitting properly on their hips and shoulders before you hop in the front seat, they are in complete control of their seating position for the drive. They can tuck the shoulder portion of the belt behind them. They can decide to unbuckle themselves to reach the Goldfish they dropped on the floor. They can fall asleep and flop completely over the side of their booster. When they get out of the vehicle and pop back in, they can neglect to re-buckle in their booster seat, turning it into a projectile when you drive away, or they can forget to look for oncoming traffic when opening their door.

Children mature at different rates. If your child meets the weight and height minimums to use a booster seat, you need to be confident that they are mature enough to be in charge of their own safety. This graphic from Car Seats for the Littles says it all:


Sitting properly in a vehicle when you have control over the seat belt is something to be learned, and we all know that impulse control is not strong in the young ones! Just the other day, Cub randomly decided to open his car door while we were driving (slowly, thank goodness) in our neighbourhood. I usually have the child-lock on, but had deactivated it for—what else—a car seat install. I remember as a kid, likely not sitting in a booster, pretending one day that my seat belt was buckled but actually just holding it in place on my lap for the whole ride. Why? I have no idea. I was getting a kick out of the fact that I was breaking a rule, I guess. (Sorry, mom! And just in case she feels guilty she didn’t notice, it was definitely only my dad and me in the car.)There will be children who are five years old and can absolutely handle boostering. Hermione Granger would’ve been booster-ready at five, I’m sure. Other kids might not be ready until they’re six or seven. Some six-year-olds who regularly ride in a booster may prefer to switch back to a harnessed seat for road trips!

If your child outgrows their forward-facing car seat before they are mature enough to use a booster seat, you can buy a combination seat. This is a forward-facing, harnessed seat that transforms into a booster seat when the child is ready.

2- Booster seats are not a one-size-fits-all-kids-and-all-vehicles child restraint.

I always thought booster seats were such simple devices: let your booster-ready kid pick one in a cute pattern, plop it on your seat and away you go. Oh, how wrong I was. There are two types of booster seats: high-backed boosters (HBB) and backless boosters. (Many HBBs have a removable back to transform them into a backless booster when the child is older.)

HBBs have a headrest and a seat belt guide through which you feed the shoulder belt, placing the belt at the right position on your child’s collarbone. Some combinations of HBBs and the position of a vehicle’s seat belt will not allow the shoulder belt to retract properly over the child. Some vehicle shoulder belt are so far forward of the vehicle seat that when used with a backless booster, the shoulder belt cannot sit properly against the child’s collarbone. Sometimes vehicle headrests interfere with the booster sitting flush against the seat. Some kids are more comfortable in one model over another, depending on their body shape.


Try before you buy. Once you have a couple of seats in mind, you can ask in a CPST-run Facebook group if there are any incompatibilities you need to be aware of.

3- Booster seats are not necessarily easier to install or use than harnessed car seats.

Booster seat “installation” is actually more complicated than placing the booster on the vehicle seat. Go through the manuals for both the booster and your vehicle thoroughly to check for things like reclining the vehicle seat and how the vehicle’s headrests should be positioned. If you have an HBB with an adjustable headrest, check to see where the headrest should be in relation to your child’s head, and remember to move it up as your child grows. Your booster manual should also specify if you are allowed to use the UAS anchors to secure the seat. (Remember, this is only meant to hold the seat in position, it does not restrain the child.)

Then, it’s time to position your child properly in their booster. Your manual will have diagrams showing where the seatbelt must sit on their body. If the seat belt is not sitting properly on them, they are not safe in their booster seat.


Backless boosters also come with a shoulder belt positioning clip. This is a little clip that is placed on the vehicle seat belt to position the shoulder belt on the child. Your manual will explain when and how to use it!


4- Most children are ten or older before they are big enough to stop using a booster.

I’m sure that none of us rode in booster seats much past four or five years old. Here’s me in mine at about age four, in the front seat of my grandparents’ camper van!

The thing is, vehicle seat belts were designed to restrain adults. Adults are bigger than children, and adults have a fully developed skeletal system. Put your kid in the car in just the seat belt. You’re probably going to notice the lap portion of the belt sitting on their tummy and the shoulder portion somewhere around their face.


Let’s just think for a second about that lap belt sitting over a child’s tummy (rather than on their hip bones). In a collision, the child’s body will move forward and the lap belt will be pushed into their tummy because the only bones there to stop it are their … backbones. So, yes, abdominal injury is a significant concern for a child using an adult seat belt and no booster seat.

A child who can sit safely without a booster is called a “5-stepper” in car seat tech parlance. They meet these 5 criteria:

5- Not all 3-in-1 car seats work well as boosters.

It can seem like an awesome investment to get a car seat that can be used rear-facing, forward-facing and as a booster. In theory, it could be the only car seat your child ever needs! These seats are commonly referred to as “3-in-1s.”

Alas, many 3-in-1s do not make good boosters. Do your research! Our 3-in-1 seat will not be usable for us as a booster seat. (It’s a Radian, and unbeknownst to me, Radians do not work for most kids as booster seats because most children will outgrow the seat for height before they ever reach the 22 kg (50 lb) weight minimum for booster use.) It may be better for your budget to get a seat that lasts a long time in forward-facing mode, and when it is booster time, purchase a dedicated booster for around $30–$80.

Bonus booster info:

  • Like car seats, booster seats expire.

Check your seat manual or the seat itself for an expiry date. If you are in Calgary, you can have your expired car seat or booster recycled at Kid Seat Recyclers!

  • Like car seats, booster seats need to be replaced after an accident.

There are a few brands that make exceptions if the seat is a minor collision that meets very specific criteria, but as a general rule, if a booster seat is in a vehicle that gets into a crash, it will need to be safely discarded and replaced. When in doubt, contact the manufacturer.

  • Even when a child no longer needs a booster seat, they should ride in the back seat until they are thirteen.

Most vehicles will specify this rule on the front passenger-seat visor and in the vehicle owner’s manual. Children should ride in the back seat. Children’s bodies are not fully developed and even an eleven-year-old who is the size of a small adult should not be seated in front of an airbag.

  • Booster laws vary by province and do not reflect best practice.

In Canada, the laws on booster use vary from province to province. As with current rear-facing laws, what’s written in the books doesn’t represent best practice. The general trend for provincial and territorial laws is that children under 18 kg must be in a car seat. Over 18 kg, British Columbia, Saskatchewan, Manitoba, Ontario, Quebec, New Brunswick, Nova Scotia, PEI and the Yukon have a specific booster law that requires children to ride in a booster until a certain weight, height or age. (For those that specify a height or weight, it is always 145 cm (4’9″) or 36 kg (80 lbs). The age requirement varies between seven and ten years old.) If we take a look at Alberta’s law, which does not require the use of a booster, the law does require what is called “proper use.” In other words, the seat belt must be used properly by all vehicle occupants:

Seat belts must be worn correctly, using the complete seat belt assembly, which means the lap belt is across the top of the hips and the shoulder belt goes across the chest. Shoulder belts cannot be behind occupant’s backs or underneath arms.”

There is no 18 kg six-year-old who is the right size to wear a seat belt correctly. Therefore, a booster seat is required, even if there is no explicit booster seat law. Alberta Health has recently updated their child passenger recommendations, and their Booster Seat YES Test advises parents to keep their child in a harnessed seat until that seat is outgrown. This is good, but not great. If a three-year-old outgrows their harnessed seat, they should not be put into a booster!

Experts are calling for unified booster laws in Canada to keep kids safe.

  • Booster seats are not inherently less safe than harnessed seats.

I don’t want people to finish reading this post thinking they must keep their child harnessed until they hit university. Boosters are not dangerous when used correctly, and the difference between correct car seat use and correct booster use is that the latter relies heavily on the child’s maturity. CPSTs often refer to the transition to a booster seat as “booster training.” You will know better than anyone else if your child can handle the responsibility, so focus less on age, weight and height milestones and more on whether your child can comprehend the consequences of not staying properly seated.


And I know many adults will read about booster-seat-readiness and think that they don’t even sit properly in a vehicle 100% of the time. Honestly, we really should try! But the good news is that adult’s bodies are fully developed and can better withstand the forces of a collision. I can assure you that since taking my CPST training, I have eliminated a bunch of my bad habits and now pay attention to how I am sitting both as a passenger and a driver so that my seat belt can do its job if ever it needs to. Hopefully you will do the same!


  • Booster seats cannot be installed with only a lap belt.

You cannot use a booster seat in a vehicle position with only a lap belt. Remember this when choosing seating positions when you have multiple children. While you can install a car seat using only a lap belt, booster seats require a lap/shoulder belt.

Additional resources:

CPST-recommended Comination (harnessed-to-booster) Seats

CPST-recommended Dedicated Booster Seats

Harness, Booster or Belt Decision Tree

Car Seats for the Littles: Proper Booster Fit



3 responses to “5 Things I Didn’t Know About Booster Seats”

  1. Sarah

    You made a comment about some seats not fitting with the headrests on a car. Can the car headrest be removed to get a good install? How would I know whether this is or isn’t allowed?

    1. Lindsay

      Hi Sarah. You will need to check your vehicle owner’s manual for this information, usually found in the section on car seats. Failing that, you should contact your vehicle manufacturer to ask them if it is acceptable to remove the headrest for a car seat or booster install, or ask a CPST to look it up in their LATCH manual (a manual which has most of the car seat installation information from all major car makers!). Hope that helps!

  2. My 6.5-year-old is still in a harness car seat. She can buckle and unbuckle herself, but she is small so she is staying in the car seat as long as possible.

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Welcome to my Wolf Pack!

My name is Lindsay and I am a 40-year-old mama of four trying to live an eco-friendly, budget-friendly life! I am a substitute teacher and Child Passenger Safety technician in Calgary, Alberta. Join me on my adventures!

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