Choosing a car seat is an important decision, but using and installing it correctly is just as important.
Even seemingly small mistakes -such as leaving a harness too loose, putting a child into their car seat wearing bulky clothing, or installing a seat incorrectly - can affect how effectively the restraint can protect your child.
At Pramworld, we know that car seat safety can sometimes feel overwhelming, especially with different regulations, installation methods and terminology to navigate. That's why we've put together some of the most common car seat safety mistakes, using guidance from leading car-seat manufacturers and UK government advice.
Important: Always follow the instructions supplied with your specific car seat and vehicle. If you're unsure whether your seat is correctly fitted, seek advice from a qualified car-seat expert.
- Not checking that the car seat is suitable for your child
One of the first mistakes to avoid is choosing a car seat based purely on age.
Under current UK rules, children normally need to use a child car seat until they are 12 years old or 135cm tall, whichever comes first. The appropriate seat depends on the child's height or weight, depending on the type of restraint.
For R129-approved height-based seats, the child's height is particularly important. The seat must be suitable for your child's height range, and the manufacturer's maximum weight limits must also be followed where applicable.
The mistake: Assuming that a particular age automatically means your child is ready for the next stage.
The safer approach: Check your child's current height and/or weight against the limits of the particular car seat, depending on how that seat is approved, and always follow the manufacturer's instructions.
- Installing the car seat incorrectly
A car seat needs to be installed according to its instructions to work as intended.
This isn't simply about getting the seat to "look right". Different seats use different installation methods, and some require additional features such as a support leg, tether straps or a particular belt route.
BeSafe's Stretch instructions, for example, state that incorrect installation could endanger a child and tell parents to follow both the car-seat instructions and the vehicle manual.
Axkid similarly advises parents to check the vehicle manufacturer's approved seating positions. For some of its seats, tether straps are also an essential part of the installation.
Avionaut also advises checking that a particular car seat can be properly installed in your specific vehicle before purchase.
The mistake:
Assuming that because a seat is attached to the car, it must be correctly installed.
What to do instead:
Read the car-seat manual and vehicle manual, check compatibility and follow every installation step for your particular model.
- Not tightening the harness enough
A harness should sit snugly against your child and should not have unnecessary slack.
The exact method for checking harness tension varies between car-seat models, so always follow the instructions supplied with your particular seat. For example, Maxi-Cosi advises that one finger should fit between the harness and the child's chest, while Nuna recommends a pinch test on applicable seats. BeSafe provides its own specific harness-tightening guidance.
The mistake:
Doing up the harness without checking whether it is actually snug against your child.
What to do instead:
Position your child correctly against the seat and tighten the harness according to the instructions for your specific model.
- Putting your child in their car seat wearing a bulky coat
This is particularly easy to get wrong during autumn and winter.
A thick coat or padded snowsuit can create extra space between your child's body and the harness. The material can compress in a collision, potentially leaving the harness less snug.
BeSafe's Stretch manual specifically states:
"Avoid puffy clothes since this prevents being able to tighten the belts fully."
Britax Römer gives similar advice, explaining that a very thick coat can prevent the harness or seat belt from being tightened sufficiently. It recommends removing very thick coats and using a blanket over the harness if additional warmth is needed.
CYBEX also advises against thick clothing such as winter jackets and recommends thin, well-fitted clothing so the restraint can sit correctly against the child.
The mistake:
Putting your child into the car seat with their thick winter coat already on.
What to do instead:
Remove bulky outerwear before securing your child. If your child needs extra warmth, follow your car-seat manufacturer's guidance -this may include placing a blanket over the correctly fastened harness.
- Leaving the harness twisted
A harness should lie flat against your child.
Twisted straps can affect how the restraint sits on the child, so this is something worth checking every time you buckle them in.
BeSafe specifically states that its harness straps must not be twisted, while Maxi-Cosi advises checking that the harness is at the correct height and that the straps aren't twisted.
Avionaut's guidance also tells parents to make sure the harness is correctly positioned and that straps are not underneath the child's back.
The mistake:
Buckling your child in quickly without checking the straps.
What to do instead:
Before setting off, check that the harness is flat, correctly positioned and securely fastened according to your seat's instructions.
- Moving your child forward-facing too soon
This is an area where it's important to distinguish the legal minimum from manufacturer recommendations.
Under UK law, R129 height-based seats must be rear-facing until the child is over 15 months old.
However, several manufacturers recommend keeping children rear-facing beyond this minimum where the seat allows.
BeSafe's Beyond², for example, is designed to allow rear-facing travel until around 6 years old, within its specified 125cm/22kg limits.
Avionaut also promotes rear-facing travel and offers models specifically designed for extended rear-facing use.
The mistake:
The mistake: Assuming that reaching 15 months means your child must immediately move to a forward-facing seat.
What to do instead:
Check the rear-facing limits of your specific seat. Some seats are designed to allow rear-facing travel well beyond the legal minimum. If your seat permits longer rear-facing use, follow the manufacturer's instructions and limits.
- Forgetting about the airbag
A rear-facing car seat must not be placed in front of an active frontal airbag.
This is a legal requirement in the UK. GOV.UK states that front airbags must be deactivated before fitting a rear-facing baby seat in a front seat.
BeSafe's Stretch instructions are equally clear, stating that the seat must not be installed in a front seat with an activated airbag.
Britax Römer also states that rearward-facing car seats can only be installed in the front passenger seat when the airbag is deactivated.
Avionaut gives the same warning in its Cosmo instructions.
The mistake:
Installing a rear-facing seat in the front passenger seat without checking the airbag.
What to do instead:
Follow your vehicle and car-seat manufacturer's instructions when choosing a seating position. A rear-facing seat must not be installed in front of an active frontal airbag.
- Assuming ISOFIX automatically means the installation is correct
ISOFIX does not remove the need to follow the full installation instructions. Depending on the seat, there may be additional installation requirements such as a support leg, tether straps or installation indicators.
Axkid, for example, states that tether straps must be used on its relevant ISOFIX installations.
BeSafe's Stretch is an example of a seat designed to be installed using a vehicle seat belt rather than ISOFIX, showing why parents shouldn't assume that one installation method is automatically appropriate for every seat or car.
The mistake:
Assuming that hearing the ISOFIX connectors click into place means the installation is finished.
What to do instead:
Follow the complete installation procedure for your specific seat, including checking indicators, support legs, tether straps or other required components.
- Using unapproved accessories or modifying the seat
It can be tempting to add extra padding, inserts, covers or accessories to make a car seat more comfortable.
However, car seats are safety products and shouldn't be modified without the manufacturer's approval.
Avionaut's Cosmo manual, for example, specifically warns:
"Do not modify the Avionaut Cosmo child safety seat in any way, as it may affect the child's safety during its use."
The same principle applies to accessories: check whether an accessory is approved for your specific car seat before using it.
The mistake:
Adding aftermarket padding or accessories because they appear to improve comfort.
What to do instead:
Only use inserts, covers and accessories in accordance with your car-seat manufacturer's instructions.
- Forgetting to check the seat as your child grows
A car seat isn't something you fit once and then forget about.
As your child grows, check whether the harness, headrest and other adjustable parts need to be repositioned according to your specific car-seat instructions.
Axkid recommends checking that the headrest is correctly positioned as the child grows and explains that the correct position is important for side-impact protection.
Avionaut's instructions similarly emphasise that harness height should be determined by the child's shoulder position rather than simply relying on an age-based assumption.
BeSafe's Beyond² includes an adjustable headrest designed to grow with the child up to its 125cm limit.
The mistake:
Leaving the harness and headrest in the same position for months because they "still look fine".
What to do instead:
Regularly check your child's height and weight against the seat's limits and adjust the harness and headrest according to the manufacturer's instructions.
Bonus: Buying a second-hand car seat without knowing its history
A car seat may have been involved in a collision without showing obvious signs of damage. If you don't know the complete history of a second-hand seat, you can't be certain it hasn't been involved in an accident or otherwise damaged.
Britax Römer advises against using a second-hand car seat when its history is unknown.
If you're buying a used seat, make sure you know its complete history and can verify that it has not been involved in a collision, and check that it is still within the manufacturer's recommended period of use.
Car Seat Safety Checklist
Before every journey, take a few seconds to check:
✓ Is the seat suitable for my child's current height and/or weight, according to the manufacturer's instructions?
✓ Is the seat compatible with my vehicle and seating position?
✓ Has it been installed according to the manufacturer's instructions?
✓ Is the harness snug against my child?
✓ Are the harness straps flat and untwisted?
✓ Is the headrest correctly positioned?
✓ Is my child wearing thin clothing rather than a bulky coat?
✓ Am I only using approved inserts and accessories?
✓ If the seat is rear-facing in the front passenger seat, has the airbag been deactivated?
✓ Are loose items securely stored?
Need help with your car seat?
Car-seat safety can feel complicated, particularly when you're comparing different installation methods, height limits, harness systems and stages.
If you're unsure, don't guess.
Always start by checking the manual for your specific car seat and your vehicle. If you're still unsure about compatibility, installation or which seat is suitable for your child, speak to a qualified car-seat expert.
At Pramworld, our car-seat experts can help you with car-seat advice, from choosing a suitable seat through to understanding installation and fit.
Need car-seat advice? Get in touch with our team.
Important safety information
This article provides general information and does not replace the instructions supplied with your specific car seat or vehicle. Car-seat features, installation requirements and usage limits vary between models. Always follow the manufacturer's instructions and current UK requirements. If you are unsure about the correct car seat or how to install it, seek advice from a qualified car-seat specialist.