Knowing when to move your child into a toddler car seat is a big milestone for parents. Many families wonder whether it’s based on age, weight, height, or simply when their baby looks uncomfortable in their current seat.
The truth is, the right time to move to a toddler car seat depends on your child’s size and the limits of their current seat — not their birthday.
Read on to find out When to Move to a Toddler Car Seat: Age, Weight & Height Explained (UK)
This guide explains exactly when to move to a toddler car seat, what to look for, and how to choose the safest next-stage seat for your child.
When Should You Move to a Toddler Car Seat?
However, there is no set age. The only safe time to move is when your child has outgrown their infant carrier.
You should move to a toddler car seat when:
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Your child exceeds the maximum height of their baby seat
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Your child exceeds the maximum weight of their baby seat
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Their head is close to the top of the shell
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The harness no longer fits correctly
Moving too early can be dangerous. Moving too late can also be unsafe if your child has exceeded the seat’s limits.
UK Toddler Car Seat Rules Explained
In the UK, children must use a car seat until they are 12 years old or 135cm tall, whichever comes first.
Most modern toddler car seats follow the R129 (i-Size) regulation, which uses your child’s height rather than weight.
Key rules for parents:
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Children must travel rear-facing until at least 15 months
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Your child must stay within the height limits of the seat
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The seat must be approved for your car
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The seat must be installed correctly
Rear-facing is strongly recommended for as long as your toddler car seat allows.
Signs Your Child Has Outgrown Their Baby Car Seat
Your child is ready for a toddler car seat if:
✔ They have reached the maximum height limit
✔ They have reached the maximum weight limit
✔ Their head is within 2cm of the top of the shell
✔ The harness is becoming difficult to adjust
✔ They look cramped or uncomfortable
Never move your child into a car seat that is too big for them to “grow into”. A poor fit can reduce protection in a crash.
What Size Toddler Car Seat Does My Child Need?
Toddler car seats are sold by height range rather than age.
Common toddler car seat sizes include:
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61–105cm (approx. 6 months to 4 years)
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61–125cm (approx. 6 months to 6–7 years)
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40–105cm (birth to 4 years multi-stage seats)
Always choose a seat that fits your child now, not one they will grow into later.
If you’re unsure which size is right, you can browse the full range here:
👉 Shop Toddler Car Seats
Rear-Facing or Forward-Facing Toddler Car Seats?
Rear-facing toddler car seats are far safer for young children. In a collision, they support the head, neck and spine and spread crash forces across the shell of the seat.
Although children can legally face forward from 15 months, best practice is to keep them rear-facing until at least 4 years old — and longer if your seat allows. We advocate keeping your child rear facing for as long as possible for safety reasons and would advocate for up to 6 or 7 years old where possible.
Many modern toddler car seats now support rear-facing travel up to 125cm, which is around 6 or 7 years old.
What Are Your Toddler Car Seat Options?
There are three main types of toddler car seats available:
1. Rotating Toddler Car Seats (61–105cm)
These seats rotate towards the car door, making it easier to lift your child in and out.
Popular options include:
2. Extended Rear-Facing Toddler Car Seats (61–125cm)
These allow your child to remain rear-facing for much longer.
Popular options include:
3. Multi-Stage Toddler Car Seats (40–105cm)
These grow with your child from birth through toddlerhood to 6/7 years old and beyond.
Popular options include:
How to Choose the Right Toddler Car Seat
Use this simple checklist:
✔ Fits your child’s current height and weight
✔ Compatible with your car
✔ Supports rear-facing for as long as possible
✔ Easy to use every day
✔ Comfortable for long journeys
✔ Fits alongside other seats if needed
Before buying, always check compatibility:
👉 Car Seat Compatibility & Fitting Lists
Why Professional Fitting Matters
A toddler car seat is only safe if it is fitted correctly. Even the best seat in the world cannot protect your child if it is installed incorrectly.
Common fitting mistakes include:
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Loose ISOFIX connection
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Incorrect seatbelt routing
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Incorrect recline angle
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Harness not tightened properly
You can book a professional fitting appointment here:
👉 Car Seat Fitting Service
Recommended Toddler Car Seats from In Car Safety Centre
Here are some of the most trusted toddler car seats available today:
Best Rotating Toddler Car Seats
Best Extended Rear-Facing Toddler Car Seats
Best Multi-Stage Toddler Car Seats
View the full range here:
👉 https://incarsafetycentre.co.uk/collections/shop-for-toddlers
👉 https://incarsafetycentre.co.uk/collections/car-seats
Final Thoughts
Moving your child into a toddler car seat is an important step in their safety journey. The right seat, fitted correctly and used properly, gives your child the best possible protection on every journey.
If you want expert advice and peace of mind, the team at In Car Safety Centre are ready to help.
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