• Black booster car seat with green belt guides, StepUp label shown from multiple angles
  • Black booster car seat with green side armrests and StepUp label, child seated
  • Black booster car seat with green belt guide, with a child seated inside
  • Black booster car seat with green headrest guides and side wings, StepUp
  • For Your Little One Stepup I-Size Isofix 2/3 Car Seat Booster Seat - Slate Mist (4-12 Years)
  • Dark gray i-Size booster car seat with green side supports and ISOFIX base, side view.
  • Dark gray i-Size booster car seat with green armrest tabs and ISOFIX base, rear view.
  • Dark gray i-Size booster car seat with green head and side supports, angled rear view.
  • Dark gray i-Size booster car seat with green head support and ISOFIX base, side view.
  • Dark gray i-Size booster car seat with green armrest, ISOFIX base and label on side.
  • Dark gray i-Size booster car seat with green head support and ISOFIX base, side view.
  • Dark gray i-Size booster car seat with green accents, centered rear view.
  • Dark gray i-Size booster car seat with green accents, rear view with logo on headrest.
  • Dark gray i-Size booster car seat with green armrest detail and ISOFIX base, angled view.
  • Black booster car seat with green belt guide pads and instruction panel
  • Dark gray i-Size booster car seat with green arm and head supports, front-left view.
For Your Little One

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

Good to know i-Size ISOFIX Group 2/3 | Secure Click-In Fit | 4–12 Years
£49.99 £79.99 Save 37% In stock

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Suitable for children 100–150cm in height (approx. 4–12 years)

Group 2: 15–25kg (approx. 4–6 years) — Forward-facing
Group 3: 22–36kg (approx. 6–12 years) — High-back booster mode

Installation: ISOFIX — check your vehicle is ISOFIX compatible before purchase
Always check your child's height against the seat's headrest guide before use
1x Stepup i-Size ISOFIX Car Seat (Slate Mist)
1x User Manual
✔ i-Size (R129) Certified — Exceeds current EU safety regulations
✔ Rigid ISOFIX connection — click-in installation eliminates fitting errors
✔ Fits children 100–150cm (approx. 4–12 years) — Group 2 & 3
✔ Deep padded side-impact protection wings
✔ One-hand adjustable headrest — multiple height positions, no tools needed
✔ Premium breathable padding for all-day comfort
✔ Removable, machine-washable seat cover

For Your Little One Stepup i-Size ISOFIX Group 2/3 Car Seat — Slate Mist. Designed to keep your child safe and comfortable from 100 cm to 150 cm (approximately 4 to 12 years), the Stepup i-Size ISOFIX car seat is the last car seat you'll ever need to buy for this stage. Built to the latest UN R129 i-Size safety standard, it delivers superior side-impact protection and a rock-solid ISOFIX connection every single time.

Why Parents Love It

  • i-Size Certified (UN R129) — Exceeds current EU safety regulations for enhanced protection
  • ISOFIX Installation — Rigid, click-in connection eliminates installation errors for total peace of mind
  • Fits 100–150 cm (approx. 4–12 years) — Grows with your child through Group 2 and Group 3 stages
  • Side-Impact Protection — Deep, padded side wings absorb and deflect impact energy away from your child
  • One-Hand Adjustable Headrest — Multiple height positions adapt quickly as your child grows, no tools required
  • Removable, Machine-Washable Cover — Easy to keep fresh and clean
  • Slate Mist Finish — Cool, contemporary grey tone that suits any car interior

Safety You Can Trust

The Stepup i-Size meets the stringent UN R129 regulation, which requires extended side-impact testing and a minimum height requirement — giving your child significantly more protection than older Group 2/3 seats. The rigid ISOFIX connection anchors the seat directly to your car's chassis, removing the risk of incorrect belt-only installation.

Comfort for Every Journey

Thick, breathable padding and a one-hand adjustable headrest with multiple height positions mean your child can settle in comfortably whether it's the school run or a long motorway trip.

Specifications

  • Safety Standard: UN R129 (i-Size)
  • Child Height: 100–150 cm
  • Approx. Age: 4–12 years
  • Installation: ISOFIX
  • Facing Direction: Forward-facing
  • Cover: Removable & machine washable
  • Colour: Slate Mist
Black booster car seat with green belt guides, StepUp label shown from multiple angles
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
Supporting families since 2011
Trusted by families across the UK
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Free UK Delivery

On UK mainland orders over £49.99

Same-Day Dispatch

Order by 2.30pm for same-day dispatch

Easy Returns

Simple returns for extra peace of mind

Why you'll love it

Designed around family life

Discover the features, thoughtful details and benefits designed to make life with little ones easier.

i-Size Safety That Exceeds the Standard
01

i-Size Safety That Exceeds the Standard

The Stepup i-Size is certified to UN R129 — the latest and most rigorous car seat safety regulation in Europe. Unlike older Group 2/3 seats, i-Size requires mandatory side-impact testing, meaning your child is protected from impacts that traditional standards don't even test for. Paired with rigid ISOFIX connectors, the seat locks directly into your car's chassis for a secure, error-free fit every time you travel.
For Your Little One Stepup I-Size Isofix 2/3 Car Seat Booster Seat - Slate Mist (4-12 Years)
02

Grows With Your Child From 4 to 12 Years

Covering 100 cm to 150 cm in height, the Stepup takes your child through both Group 2 and Group 3 stages in a single seat — no mid-stage upgrades needed. The one-hand adjustable headrest moves in seconds to match your child's growing height, while the deep padded side wings reposition automatically to keep protection exactly where it's needed at every stage.
Comfort Built for Real Family Life
03

Comfort Built for Real Family Life

The breathable, premium-padded cover keeps them cool in summer and cosy in winter — and when it needs a refresh, simply remove it and pop it in the washing machine at 30°C. The cool Slate Mist finish brings a contemporary, understated style to any car interior and pairs effortlessly with modern family vehicles.
Designed for family life Comfort & practicality Made for everyday adventures

Customers praised this I-Size ISOFIX booster seat for being "sturdy," "comfortable," and "well made." Reviewers highlighted "easy to fit" ISOFIX installation, "nice padding," and the attractive Slate Mist color. Parents appreciated comfort on longer journeys and quick delivery. No negative feedback was reported across reviews.

  • Really impressed with how sturdy this feels. My child is comfortable even on longer journeys.
  • The finish is really nice and it feels well made all round. Happy with the purchase.
  • A really good booster seat for our needs. Easy to fit and looks good too.
  • 5 stars: 67 (100%)
  • 4 stars: 0 (0%)
  • 3 stars: 0 (0%)
  • 2 stars: 0 (0%)
  • 1 star: 0 (0%)
S
Sarah M.
Fast delivery

Ordered in the afternoon and it arrived really quickly. Well packed and the seat was exactly as described when it arrived.

D
David B.
Nice padding

The padding feels comfortable and the seat is supportive. Very pleased so far.

L
Leah W.
Good quality finish

The finish is really nice and it feels well made all round. Happy with the purchase.

D
Daniel C.
Great quality

Really impressed with how sturdy this feels. My child is comfortable even on longer journeys.

K
Katie W.
Great little booster

A really good booster seat for our needs. Easy to fit and looks good too.

T
Tom D.
Arrived quickly

Delivery was very quick and everything arrived well packed. No issues at all.

E
Emily T.
Simple to install

Used it on a long trip already and there were no complaints. Comfortable seat and easy to buckle in.

M
Michael E.
Delivery was quick

Really pleased with the delivery speed and the seat arrived in great condition.

C
Chloe B.
Good support

Comfortable seat and good support for longer journeys. It feels sturdy and well made.

J
James W.
Solid and comfortable

Easy to get fitted with the ISOFIX and it sits nicely in the car. Feels secure and well made.

H
Hannah S.
Helpful and quick support

Contacted support about a small question and they were very helpful and got it resolved quickly.

S
Sam R.
Exactly as expected

The seat is exactly as described and was easy to fit. Very happy with how it feels in the car.

L
Laura B.
Great booster seat

A lovely booster seat and much nicer than I expected for the price. Feels supportive and well made.

O
Oliver D.
Very good seat

Good quality, comfortable and easy to use. Very happy with this one.

M
Megan W.
Great for an older child

A really good option for an older child. It feels supportive without being too bulky.

M
Michael H.
Very happy

Really pleased with this seat. It looks smart in the car and my child seems very comfortable.

R
Rachel W.
No complaints

My child is happy with it, which is the main thing. It is comfortable and easy to buckle in.

J
Joe H.
Easy fitting

The ISOFIX fitting is simple and the seat was ready to use very quickly. Great for busy mornings.

S
Sophie T.
Lovely colour

The Slate Mist colour is really nice and the seat feels great quality. Very happy with it.

A
Adam C.
Great colour and quality

The Slate Mist colour is lovely and the overall quality feels excellent.

L
Lauren B.
Lovely booster seat

Really nice booster seat with a good amount of padding. My child seems very comfortable.

O
Oliver B.
Easy to use

Nice and straightforward to fit and use. The ISOFIX makes it really easy to get into position.

L
Laura G.
Easy to install

Simple to install with the ISOFIX and it sits nicely once fitted. Very pleased.

M
Mark Y.
Good purchase

Very pleased overall. It arrived quickly, was easy to fit and feels secure.

H
Hannah C.
Perfect for us

Exactly what we needed for our older child. Comfortable, sturdy and not too bulky.

C
Chris H.
Really good purchase

Good quality booster seat and it feels secure in the car. Would buy again.

S
Sophie A.
Helpful customer support

I contacted support with a question and they were really helpful. It was sorted out quickly and the seat is great.

J
Jack M.
Well made

Feels like a really solid seat and the padding is comfortable. Good quality overall.

J
Jessica M.
Exactly what we needed

It fits well, looks good and is comfortable for our child. Exactly what we were after.

D
Daniel S.
Support answered quickly

Had a quick question about fitting and customer support came back to me promptly. Really helpful.

R
Rebecca F.
Good value

Very pleased with the seat for the price. It feels much better made than some we looked at.

M
Matthew L.
Great service

Delivery was quick and customer support were helpful when I had a question. Everything was sorted quickly.

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