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i-Size Car Seats

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31 products
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Latte beige car seat set showing infant and toddler modes, side-by-side Latte beige car seat set showing infant and toddler modes, side-by-side
Sold out

For Your Little One

For Your Little One GrowWithMe 0/1/2/3 i-Size Car Seat - Latte Beige (Birth-12 Years)-Grade A

£55.00
£55.00 -54%
£119.99
Black booster car seat with green belt guides, StepUp label shown from multiple angles Black booster car seat with green belt guides, StepUp label shown from multiple angles

For Your Little One

For Your Little One Stepup I-Size Isofix 2/3 Car Seat Booster Seat - Slate Mist (4-12 Years)

£49.99
£49.99 -37%
£79.99
5.0
(67 reviews)
For Your Little One AllStage 360 0/1/2/3 ISOFIX I - Size Car Seat - Midnight Black (Birth - 12 Years) - For Your Little One For Your Little One AllStage 360 0/1/2/3 ISOFIX I - Size Car Seat - Midnight Black (Birth - 12 Years) - For Your Little One
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Clearance

For Your Little One

For Your Little One AllStage 360 0/1/2/3 ISOFIX I-Size Car Seat - Midnight Black (Birth-12 Years)-Grade A Return

£70.00
£70.00 -53%
£149.99
5.0
(1 reviews)
For Your Little One AllStage 360 0/1/2/3 ISOFIX I - Size Car Seat - Slate Mist (Birth - 12 Years) - For Your Little One For Your Little One AllStage 360 0/1/2/3 ISOFIX I - Size Car Seat - Slate Mist (Birth - 12 Years) - For Your Little One
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Clearance

For Your Little One

For Your Little One AllStage 360 0/1/2/3 ISOFIX I-Size Car Seat - Slate Mist (Birth-12 Years)-Grade A Return

£75.00
£75.00 -49%
£149.99
For Your Little One AllStage 360 0/1/2/3 ISOFIX I - Size Car Seat - Midnight Black (Birth - 12 Years) - For Your Little One For Your Little One AllStage 360 0/1/2/3 ISOFIX I - Size Car Seat - Midnight Black (Birth - 12 Years) - For Your Little One
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For Your Little One

For Your Little One AllStage 360 0/1/2/3 ISOFIX I-Size Car Seat - Midnight Black-Damaged box

£75.00
£75.00 -49%
£149.99
Blush rose 2/3 booster car seat with headrest, armrests, and green belt guides Blush rose 2/3 booster car seat with headrest, armrests, and green belt guides
Sold out

For Your Little One

For Your Little One Stepup I-Size Belted 2/3 Car Seat Booster Seat - Blush Rose (4-12 Years)

£34.99
£34.99 -50%
£69.99
5.0
(25 reviews)
Black grow-with car seat set shown in multiple angles, including base and harness front Black grow-with car seat set shown in multiple angles, including base and harness front
Sold out

For Your Little One

For Your Little One GrowWithMe 0/1/2/3 i-Size Car Seat - Midnight Black (Birth-12 Years) -Grade A

£55.00
£55.00 -54%
£119.99
Black high-back car seat with padded headrest, side wings, and green adjustment pads Black high-back car seat with padded headrest, side wings, and green adjustment pads

For Your Little One

For Your Little One Stepup I-Size Isofix 2/3 Car Seat Booster Seat - Midnight Black (4-12 Years)

£49.99
£49.99 -37%
£79.99
5.0
(57 reviews)
Blush rose high-back booster car seat with padded headrest and side armrests Blush rose high-back booster car seat with padded headrest and side armrests

For Your Little One

For Your Little One Stepup I-Size Isofix 2/3 Car Seat Booster Seat - Blush Rose (4-12 Years)

£49.99
£49.99 -37%
£79.99
5.0
(24 reviews)
Latte beige AllStage 360 car seat shown from multiple angles with rotating base Latte beige AllStage 360 car seat shown from multiple angles with rotating base
Sold out

For Your Little One

For Your Little One AllStage 360 0/1/2/3 ISOFIX I-Size Car Seat - Latte Beige (Birth-12 Years)-Grade A return

£70.00
£70.00 -53%
£149.99
For Your Little One AllStage 360 0/1/2/3 ISOFIX I - Size Car Seat - Blush Rose (Birth - 12 Years) - For Your Little One For Your Little One AllStage 360 0/1/2/3 ISOFIX I - Size Car Seat - Blush Rose (Birth - 12 Years) - For Your Little One
Sold out
Clearance

For Your Little One

For Your Little One AllStage 360 0/1/2/3 ISOFIX I-Size Car Seat - Blush Rose (Birth-12 Years)-Grade A Return

£70.00
£70.00 -53%
£149.99
5.0
(1 reviews)
Belted booster car seat set with headrest, side wings, and green belt guides Belted booster car seat set with headrest, side wings, and green belt guides
Sold out

For Your Little One

For Your Little One Stepup I-Size Belted 2/3 Car Seat Booster Seat - Midnight Black (4-12 Years)

£34.99
£34.99 -50%
£69.99
5.0
(38 reviews)

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i-Size Car Seats - For Your Little One
i-Size Car Seats
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Discover i-Size Car Seats

i-Size Car Seats – The Safest Standard for Every Stage

Shop our range of i-Size (R129) car seats – the latest and most stringent European car seat safety standard, offering significantly improved protection over the older Group system. All i-Size car seats in our range are ISOFIX compatible and meet the current UK and European R129 regulation. Free UK delivery available.

What Is i-Size?

i-Size (also known as R129) is the newer European car seat safety regulation that replaced the older ECE R44 Group system. Key improvements over the older standard include:

  • Height-based classification – i-Size seats are classified by your child's height rather than weight, making it easier to know when your child has outgrown a seat.
  • Mandatory rear-facing until 15 months – All i-Size seats must keep children rear-facing until at least 15 months, significantly improving safety for young children.
  • Enhanced side-impact testing – i-Size seats must pass more rigorous side-impact crash tests than older Group seats.
  • ISOFIX required – All i-Size seats must use ISOFIX installation, providing a rigid, secure connection to the car.

i-Size vs Group Car Seats – Which Is Safer?

i-Size is the safer standard. The mandatory rear-facing requirement until 15 months, enhanced side-impact testing, and compulsory ISOFIX installation all provide measurably better protection than the older Group system. If you're buying a new car seat, choose i-Size where possible.

i-Size Car Seats by Stage

  • Birth to 15 months (40–83cm) – Infant i-Size seats. Rear-facing from birth. Examples: Cybex Cloud T, Doona i.
  • Birth to 4 years (40–105cm) – Combination i-Size seats. Extended rear-facing. Examples: My Babiie spin seats.
  • 15 months to 12 years (76–150cm) – Toddler and child i-Size seats. Forward-facing from 15 months.

Why Choose Our i-Size Car Seats?

  • Latest R129 safety standard – The most stringent car seat regulation available
  • Mandatory rear-facing to 15 months – Maximum protection for young children
  • Enhanced side-impact protection – Rigorously tested beyond older standards
  • ISOFIX installation – Rigid, secure connection to your car
  • Height-based sizing – Easy to know when your child has outgrown the seat

Complete Your Car Seat Setup

Browse our ISOFIX bases, car seat footmuffs, car seat raincovers, and our full car seat types guide.

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Need to know

Frequently asked questions

Helpful answers to some of the questions our customers ask most often.

An i-Size car seat (also known as R129) is a car seat that meets the latest European safety regulation, which replaced the older ECE R44 Group system. i-Size seats are classified by your child's height rather than weight, must keep children rear-facing until at least 15 months, must use ISOFIX installation, and must pass more rigorous side-impact crash tests than older Group seats. i-Size is the safer standard – if you're buying a new car seat, choose i-Size where possible.
Yes – i-Size (R129) is the safer standard. The key improvements over the older Group (ECE R44) system are: mandatory rear-facing until at least 15 months (significantly safer for young children), enhanced side-impact testing, compulsory ISOFIX installation (safer and more convenient than seatbelt installation), and height-based classification (easier to know when your child has outgrown the seat). Both standards are legal in the UK, but i-Size provides measurably better protection.
All i-Size car seats require ISOFIX installation – this is a mandatory requirement of the R129 regulation. Some i-Size seats have built-in ISOFIX connectors that attach directly to your car's ISOFIX anchor points; others require a separate ISOFIX base that the car seat clicks into. An ISOFIX base provides a more rigid, secure installation and makes it easier to transfer the car seat between cars. Check whether an ISOFIX base is included with your chosen seat or needs to be purchased separately.
Still have a question? Our customer care team is here to help.

Helpful advice

i-Size Car Seats Buying Guides

Helpful guides to make choosing the right products for your little one a little easier.

ISOFIX Car Seats: What Parents Need to Know 01

Buying guide

ISOFIX Car Seats: What Parents Need to Know

Understand how ISOFIX car seats and bases work, what compatibility means and how to check the installation before every journey.

Read the guide →
i-Size vs Group Car Seats: What’s the Difference? 02

Buying guide

i-Size vs Group Car Seats: What’s the Difference?

Understand the difference between i-Size, R129 and Group car seats, including height guidance, rear-facing use, testing and installation.

Read the guide →
More helpful advice coming soon Swipe to explore more buying guides