Car seats can feel confusing for new parents — from infant carriers and toddler seats to high-back boosters, knowing when to make the switch isn’t always straightforward. Add in changing UK laws and i-Size regulations, and it’s easy to wonder if you’re getting it right.
In this clear guide, we’ll walk you through the key signs your baby has outgrown their infant carrier, when to move up to the next stage, and how long to keep them rear-facing. We’ll also cover booster seats and share practical tips for keeping your little one warm without compromising safety.
At a glance
- Infant carrier (the “first seat”): rear-facing shell for newborns, with snug side protection for head/neck/spine.
- Legs over the edge ≠ outgrown: length of legs isn’t the trigger to switch — head position and harness slots are.
- i-Size (R129): rear-facing to at least 15 months. Many families keep rear-facing longer for added protection.
- Next stages: choose a seat that matches your child’s height (and sometimes weight) and your vehicle install method.
- Booster readiness: high-back boosters are typically used for older, taller children who can sit correctly for the whole journey.
- Warmth without bulk: a car seat blanket not interfering with the car seat safety (no coats under the straps).
Infant carrier vs. toddler/child seat — what’s the difference?
Infant carriers (Group 0/0+ or i-Size 40–75/83 cm) are deep, supportive shells designed for newborns and young babies. They prioritise side impact protection, a naturally curled newborn posture, and easy vehicle fitting (often with an ISOFIX base). Toddler/child seats are more upright, with taller shells, adjustable headrests and different harness/vehicle belt routing as children grow.
“My baby’s legs stick out — is it time to switch?”
Not necessarily. Legs over the edge are normal and safe. You should move on when:
- Baby’s head is close to or above the top of the infant carrier’s shell (check your manual’s indicator), or
- The harness slots no longer align correctly for rear-facing (usually at or just below the shoulders in infant carriers), or
- You’ve exceeded the seat’s stated height/weight limit.
How long should my child ride rear-facing?
Under the current i-Size standard (R129), children must travel rear-facing to at least 15 months. Many seats allow (and many families choose) extended rear-facing beyond that — often up to 105 cm or around age 4 — because it offers excellent protection for the head, neck and spine in a collision.
Choosing the next seat (after the infant carrier)
When your infant carrier is outgrown, look for a seat that matches your child’s height (and weight where relevant), your vehicle, and your installation preferences (ISOFIX or belt-install, swivel vs fixed). Popular next-stage categories include:
- i-Size 40–105 cm (rear-facing, sometimes rear/forward) — often used from birth or from outgrowing the infant carrier, typically with ISOFIX.
- i-Size 61–105 cm — for babies who have outgrown the carrier and are ready for a taller rear-facing shell.
- High-back booster (i-Size 100–150 cm) — for older children who can sit correctly with the adult seat belt routed through the guide. Many start this stage around 105/100 cm+
Tip: Adjustable headrests and deeper side wings help keep the head contained if your child naps in the car.
When is a booster appropriate?
A high-back booster becomes appropriate when your child is big and mature enough to sit upright correctly for the whole journey and meets the seat’s minimum height/age specification. The backrest and head wings help keep the belt in the right place and offer side protection. Plain backless boosters are generally for older, taller children in limited situations; most families prefer high-back designs for everyday use.
Installation basics you should always follow
- Read the manual first — for both the car seat and your vehicle.
- ISOFIX or seat belt: install exactly as instructed and check indicators every trip.
- Harness fit: snug “two-finger” check at the collarbone; no slack or twists.
- Clear the cabin: heavy, loose items become projectiles in a crash — secure them.
- Front airbag: if a rear-facing seat is used in front, the passenger airbag must be deactivated (and the seat moved back) per your vehicle instructions.
Keeping babies warm in the car — safely
No bulky coats or snowsuits under the harness: they compress in a crash and can leave the straps dangerously loose. Instead, use breathable layers and, for quick warmth, a car seat blanket that works with the harness.
How our car seat blanket works
- Place the blanket in the seat first and thread the straps through the built-in openings.
- Strap baby in as normal — the harness sits directly on your baby.
- Wrap over the harness when it’s cool, or leave it open when indoors/the cabin is warm.
- Quiet bow-tie closure (no noisy velcro) for undisturbed transfers.
Fabric: 100% cotton muslin outer with 1 cm hypo-allergenic fill; fits most Group 0+ seats and some Group 0+1; machine wash 30 °C (delicates), no tumble dry.
Height & stage overview (quick reference)
- Infant carrier: approx. 40–75/83 cm (rear-facing only).
- Next-stage rear-facing: e.g., 61–105 cm or 40–105 cm (often ISOFIX, sometimes swivel).
- High-back booster: typically 100–150 cm (adult belt routed through guides).
Always follow the exact limits printed on your child’s seat — those override any general guide.
FAQs
Do legs hanging over the edge mean the infant carrier is too small?
No. Look at head height relative to the shell and whether the harness slots still align correctly. Legs over the edge are common and safe.
What’s the minimum for turning forward-facing?
Under i-Size (R129), children must rear-face to at least 15 months. Many seats allow rear-facing much longer; consider extended rear-facing for added protection.
Is ISOFIX better than a belt install?
ISOFIX reduces installation error and is convenient. A correctly fitted belt-install seat is also safe — the key is following the manual exactly.
How do I keep my baby warm without a coat?
Dress in breathable layers, then add a car seat blanket over the fastened harness. Remove or open it as the cabin warms.
When can my child use just a booster cushion?
High-back boosters (with head/side support and belt guides) are preferred for most children until they fit the vehicle’s adult belt perfectly. Follow the seat’s stated height/age limits and choose a design your child can sit correctly in for the whole journey.
Final thoughts
Move up a stage when your child outgrows the seat by height or fit — not just by age. Keep rear-facing as long as your seat allows, install exactly as the manual shows, and use breathable layers with a car seat blanket for quick, coat-free warmth. Small details make a big difference to comfort and safety on every journey.
Information only (we don’t sell car seats) • Always check your car seat manual and current UK law.
