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When to Change your Child's Car Seat?

For optimum safety and protection it is vital your little one is sitting in a car seat that is suitable for their size. It’s the law that your child has to be in an appropriate car seat until they are 150cm or 36kgs, which is approx 12 years old. But it can be confusing to know when it’s time for them to move up to the next stage car seat, and with two different fitting standards and regulations it can be confusing to get your head around all the spec, jargon and statistics. We want to help you feel confident and secure in the knowledge you are choosing the appropriate car seat for your child at the right time.


Understanding the different fitting standards

Just to make things that little bit more confusing, there are currently two regulations running alongside each other which different car seats abide by. There is the “group” system and the “i-Size” system.

Let's take closer look at the two regulations –


According to RSA Ireland, the “Group” system regulation is categorised into groups depending on the weight of your child. These weight categories correspond broadly to different age groups, but it is the weight of the child that is most important when deciding what type of child restraint to use. This is how the categories are determined and act as the guide to when your child should move up to the next stage car seat. Each group has an upper weight limit, when your baby reaches this limit it is time to move them up to the next stage. Often there is an age reference within this system also, however, the size of your child is more important than their age. This is because some babies grow faster and gain weight at a quicker pace than others of the same age. Girls and boys also grow at different rates, so the focus for you to match the correct “Group Seat” should be weight. 

The “group” categories are –

Group 0+ - birth to 13kg (around 12-15months)

Group 1 – 9-18kg (around 9 months to 4.5 years)

Group 2 – 15-25kg (around 3-7 years)

Group 3 – 22-36kg (around 6-12years)

Until 2014, this was the only system for car seats in Ireland and many seats are still sold under the group system. But, with the recent introduction of the i-Size regulations there are now two regulations running alongside each other.

RSA Ireland Group Car Seats R144

RSA Car Seat Group R144


i-Size Regulations a Guide at Bygge Bo

The i-size system is the most current standard and is designed to mandate children to rear-face for at least the first 15 months or 85cm, however it is advised to rear-face for up to four years. This increases support to the child’s head, neck and vital organs and offers better protection in the event of both a frontal or side impact. In some countries such as Sweden, parents predominately rear-face their children right up to the age of 4 or more. 

The “i-Size” regulation is classified by the height and size, rather than weight, of your child. Again, there are rough age guides on the categories, but we suggest sticking to the height guides for accuracy for your child. The i-Size is developed with the Isofix system, which means the seat simply slots into anchor points that are on the car’s chassis; most vehicles from 2007 onwards will have isofix points in the rear seats. Isofix reduces the risk of human error and offers a more secure anchor connection to the vehicle. Find out more about the Isofix system here. Another key difference is child car seats approved to the older R44 regulation do not have to pass a side-impact crash test in order to be sold, whereas i-size seats must pass frontal, rear and side-impact tests.

Choosing Your Car Seat at Guide at Bygge Bo

At Bygge Bo, we encourage the use of rear-facing car seats as the safest way to travel. Rear-facing seats offer the highest safety when transporting a child in a car. According to Cybex 

The “i-Size categories are –

i-Size baby - Newborn to 85cm (0 to around 15 or 18 months) 

i-Size baby and toddler - Newborn to 105cm (0 to 4 years)

i-Size toddler and child - 61cm to 105cm (15 months to 12 years)

i-Size child - 100cm to 135cm (4 years - 12 years)


So why are there two regulations? There are two regulations because the car and car seat manufacturers require time to change their seats and fixing points in vehicles. Both regulations will continue to run alongside each other for the foreseeable future. We advise opting for an i-Size car seat for your child's first and second stage seats so that rear-facing can continue for as long as possible, which studies have proven is much safer.

So, when should you change to the next stage?

Deciding when to move your child into their next stage car seat can often be confusing, worrying about moving your child too early or late. Car seat categories often overlap, which can cause some confusion around when it really is the best time to change car seats. Children at the bottom of the weight/height group are more vulnerable to injuries. For this reason, it's better to keep them in the lowest group seat for as long as possible, rather than moving up groups too early.

We advise you to let your child reach the top limit of the group they are currently in, rather than swapping when they get the bottom weight of the next group.

As a general rule and to make it a little easier to know when it is the right time to move up a group, if your child's eyes are level with the top of the seat they are sitting in, they have outgrown their current seat. But also keep an eye on your little one's height to make sure they haven't outgrown their seat. 

Sirona Z at Bygge Bo 

Many parents think that the child has outgrown their car seat once the child's feet hang over its edge. But, only when the baby's head is out of the top of the seat is it the right time to switch to the next stage.

Selecting the seat type on your child's specific length ( and not weight) helps to avoid giving in to the temptation of premature upsizing and premature switching from rearward to forward-facing.

It can be tempting to purchase a second-hand seat; however, we always recommend buying 'new'. A car seat that has been involved in a crash can have damages or weakened points that may not be visible, and the seat may not perform as well as it should in the instance of a collision. Unless you are 100% sure of the seat's history, buying new should always be your first choice.

We know it can be confusing, which is why we're here to give you a helping hand to make your choice. Just give our expert team a call on +353469075177, and we'll talk you through it or visit our store to demo our range of car seats.

Full car seat range can also be shopped online here.

Read more about the Cybex Z-Line system here.

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