Most car seat problems aren’t dramatic. They’re small, easy-to-miss errors that creep in over time: a strap that’s slightly loose, a seat turned forward-facing a few months early, a winter coat left on under the harness. The trouble is that they can reduce how well the seat protects your child in a crash, and they’re easy to fix once you know what to look for. This guide by Babymore pulls together the most common car seat mistakes and issues in one place, explains why each one matters, and tells you how to put it right.
The most common car seat mistakes are a loose installation, a loose or badly positioned harness, turning a child forward-facing too early, leaving a bulky coat on under the straps, using accessories the manufacturer hasn’t approved, and carrying on with a seat that’s outgrown, expired, second-hand with an unknown history or been in a crash. Fix them by reading the manual, checking that the seat moves no more than about an inch at the belt path or ISOFIX points, doing the pinch test on the harness every journey, keeping your child rear-facing for as long as the seat allows, and replacing the seat when it’s outgrown, expired or has been in an accident.
This is the most common problem. A seat that isn’t fitted tightly can move too much in a crash, and the whole point of a seat is that it holds your child securely in place.
How to fix it. Follow the manual step by step. If you’re using the car’s seat belt, make sure the belt is routed through the correct guides and pulled tight, and that you’re using a seat belt with a diagonal strap (the law says you can only use a car seat in a belt without one if the seat is made for a lap belt or fitted with ISOFIX). Once it’s in, hold the seat at the belt path and give it a firm tug side to side and front to back. It should move no more than about an inch.
If your seat uses ISOFIX, check that both connectors have clicked in and that the indicators show green. Our guides on what an ISOFIX car seat is and how to fit an ISOFIX car seat properly walk you through it, and many parents find ISOFIX more consistent than belt fitting because it takes some of the guesswork out. Also check the recline: many seats have an angle indicator, and a newborn who’s too upright can slump.
Many ISOFIX seats have an extra stabilising feature. A support leg reaches from the seat down to the car floor, and a top tether strap attaches behind the seat on some forward-facing models. Both limit how far the seat can rotate or tip forward in a collision, and both are easy to forget, especially when you move the seat between cars.
How to fix it. Check your manual to see which your seat has, extend the support leg until it sits firmly on the floor with the indicator showing green, and attach and tighten the top tether if your seat has one. Make it part of your routine every time you refit the seat.
Rear-facing seats support the head, neck and spine better in a frontal crash, which is why many experts advise keeping children rear-facing for as long as the seat allows. There is also a legal minimum: under the current UK rules for height-based (i-Size) seats, your child must be rear-facing until they’re over 15 months old.
How to fix it. Treat 15 months as the minimum, not the target. Keep your child rear-facing until they reach the seat’s height or weight limit for that position, which is often well beyond the minimum. Our guide on when a baby can face forward in a car seat in the UK has more detail.
A harness that looks fine can be too loose. Over time, straps loosen, and growing children need adjustments. A loose harness lets a child move further in a crash and, in the worst case, slip out of the straps.
How to fix it. Do the pinch test every time. Once your child is buckled in and the straps are tightened, try to pinch the webbing at the collarbone. If you can grab a fold of it, tighten it until you can’t. Straps should lie flat with no twists. Our guide on how tight a car seat harness should be explains the check in more detail.
Strap height matters because it controls how your child is held. In a rear-facing seat, the straps should come through the slots at or just below your child’s shoulders. In a forward-facing seat, they should be at or just above the shoulders. Children grow fast, and straps that were right a few months ago may not be now.
How to fix it. Check the strap height whenever you check the harness, and adjust the headrest or slots as the manual describes. Many seats have a headrest that moves the straps up together as it’s raised.
A thick or puffy coat creates a layer of air between your child and the harness. When you tighten the straps over it, they feel snug, but in a crash the padding compresses and leaves slack.
How to fix it. Dress your child in thin, snug layers, secure and tighten the harness, then put a blanket or the coat over the top. For toddlers, put the coat on backwards over the harness once they’re buckled in. Our guide to car seat tips for bad weather covers this in detail, and car seat safety when the clocks go back looks at the other winter issues.
Extra padding, strap covers, inserts, sunshades and seat protectors are easy to buy, but car seats are crash-tested the way they’re designed to be used. Which? advises that adding accessories not approved by the manufacturer could compromise the seat’s safety or void the warranty, and recommends using only products supplied or recommended by the seat’s manufacturer. It also warns about specific products, such as chest clips that can put dangerous pressure on a child’s abdomen in a crash.
How to fix it. Use only the accessories that came with the seat or that the manufacturer lists as approved for your model. If you’re unsure, leave it out.
A seat that’s too small or the wrong type doesn’t protect as well. Children outgrow seats faster than most parents expect, and the signs aren’t always obvious: the top of the head level with the top of the shell, shoulders above the highest strap slots, or reaching the stated weight limit.
How to fix it. Check your seat’s height and weight limits regularly. UK seats are either height-based (i-Size, R129) or weight-based (R44), and the limits differ, so read the label. Children must normally use a car seat until they’re 12 years old or 135cm tall, whichever comes first. Our guides to understanding car seat limits, choosing a car seat and the UK car seat regulations will help you choose the right stage.
It’s tempting to move to a booster as soon as your child complains about the harness or reaches a certain age, but a harnessed seat generally offers more protection while your child still fits it.
How to fix it. Keep your child in a harnessed seat until they reach its limits, and only move to a booster when they’ve outgrown it and meet the booster’s requirements. Make sure the seat belt sits across the middle of the shoulder and low across the hips, not the stomach.
A second-hand seat may look fine and still have hidden damage from a crash, been stored badly, be missing parts or be built to older standards. You can’t tell by looking.
How to fix it. Avoid second-hand seats unless you know their full history, such as a seat from a trusted family member who can confirm it’s never been in an accident. Our guide on whether it’s safe to buy a second-hand car seat explains what to ask.
Plastics and webbing degrade over time, and manufacturers set a lifespan for each seat, often a number of years from the date of manufacture. The date is usually printed or moulded on the seat or its label.
How to fix it. Check the expiry or manufacture date in the manual or on the label, and replace the seat when it’s reached the end of its life, even if it looks fine.
Even a minor collision can cause damage you can’t see, such as stress fractures in the shell or stretched harness webbing, which could weaken the seat in a later crash.
How to fix it. Replace the seat after an accident, and check your seat’s manual and your car insurer, since some manufacturers specify what counts as a crash that requires replacement. Our article on replacing a baby’s car seat after an accident explains why.
Occasionally manufacturers recall seats because of a safety defect, and a seat that’s been recalled may be unsafe until it’s fixed or replaced.
How to fix it. Register your seat with the manufacturer so you’ll be told about any safety notices, and check the GOV.UK product safety alerts and recalls page from time to time. If you see a recall for your model, follow the manufacturer’s instructions straight away.
An airbag that goes off can strike a rear-facing seat with huge force. In the UK, you must deactivate any front airbag before fitting a rear-facing baby seat in the front passenger seat.
How to fix it. Where you can, use the back seat. Babymore’s guide to the safest position in the car for a baby’s car seat explains why the rear middle seat is often considered safest, and what to check if you do need to use the front.
Before you set off, run through this short checklist:
For more everyday habits, our baby car seat safety tips are worth a read.
Most of these mistakes come down to habits you can build in a few minutes: check the fit, check the harness, read the manual, and replace the seat when it’s outgrown, expired or been in a crash. Getting those basics right makes the biggest difference to your child’s safety on every journey.
Need a new seat? Browse Babymore’s car seats or our baby travel systems, including the MeMore travel systems, or read our guide to choosing a car seat to find the right fit for your child.
