Short answer: Use a car seat suitable for your child's height or weight on every journey, fitted exactly as the instructions say. Keep your child rear-facing for as long as the seat allows — in the UK, height-based seats must be rear-facing until at least 15 months. Never put a rear-facing seat in front of an active airbag. Avoid bulky coats under the harness, keep straps snug, and only use a second-hand seat if you know its full history. Rules differ by country, so check local law.
Of everything you buy for your child, this is the one thing that really matters if something goes wrong — and it's also where the most mistakes are made.
The rules (UK example)
- Children must normally use a child car seat until they're 12 years old or 135cm tall, whichever comes first.
- Height-based seats (labelled R129, sometimes called i-Size) must be rear-facing until your child is over 15 months.
- Weight-based seats (labelled ECE R44) are grouped by weight; group 0 and 0+ seats are rear-facing.
- Only approved seats with an “E” label can be used.
- Front seat airbags: deactivate the front passenger airbag before fitting a rear-facing baby seat in the front.
Other countries have similar rules; in the US, requirements are set by each state. If you travel, check the rules where you'll be driving.
Rear-facing for longer
Young children's heads are large and heavy compared with their bodies, and their necks are still developing. A rear-facing seat spreads crash forces across the back and head. The American Academy of Pediatrics recommends that infants and toddlers ride rear-facing for as long as possible, until they reach the highest height or weight their seat allows. The 15-month UK rule is a minimum, not a target.
“Her legs don't fit any more” isn't a reason to turn the seat round. Children sit happily with bent or crossed legs.
The most common mistakes
- Bulky coats or snowsuits under the harness. They compress in a crash and leave straps too loose. Dress your child in thinner layers, buckle them in, then put a coat or blanket over the top.
- Loose harness straps. Straps should be snug, with no slack you can pinch at the shoulder.
- Chest clip in the wrong place on seats that have one — it should sit at armpit level.
- A seat that moves. Once fitted, check it doesn't shift much at the belt path or anchor points. Use the top tether or support leg if your seat has one.
- Loose objects in the car that can become projectiles in a crash.
- Moving to a booster too soon. Keep using a harnessed seat until your child outgrows it, then a high-backed booster with a seat belt.
- Using the car seat for sleep outside the car. Car seats are for travel; once you arrive, move a sleeping baby onto a flat surface.
The back seat is safest
The AAP advises that all children younger than 13 ride in the back seat. If a child must sit in front, the seat should be moved as far back as possible — and a rear-facing seat must never face an active airbag.
Second-hand seats
Only use a second-hand seat if you know its full history, it isn't past the manufacturer's expiry date, all parts and instructions are present, and it has never been in a crash. A seat that's been in a collision can be damaged even if you can't see it. If in doubt, buy new.
Get it checked
Many retailers and local road safety services offer free fitting checks. Ask for one when you buy a seat, and again if you change cars.
Premature babies
Babies born early may need a check that they can sit safely in a semi-reclined position before discharge. Ask the neonatal team.
Related reading
Month by month: The First Year (PDF, English) guides you through your baby's first twelve months.
Sources
- GOV.UK — Child car seats: the rules.
- American Academy of Pediatrics, HealthyChildren.org — Car seats: information for families.
- RoSPA — Road safety advice.
Written by the Bloom Guides editorial team. Last updated: 20 October 2026. General information only — always follow your car seat and vehicle manufacturer's instructions and local law.