When to replace a child safety seat with a larger one?

One of the most frequently asked questions about the safety of the youngest passengers is: “When to replace a child safety seat with a larger one?” For many parents, this is a challenging issue having a huge impact on the comfort and protection of their children. Replacing a car seat for your child should be a wisely calculated step and should be based on the child’s weight and height development. So when should you do replace the seat, and when is it not required? You will find this out in the following text. Enjoy!


  • When to replace a child safety seat? Division of child safety seats based on toddler’s weight and height
  • Toddler car seat
  • When to replace a child safety seat with a larger one?
  • Car seat for older children
  • When does the use of a car seat become unnecessary?
  • When to replace a child safety seat with a larger one – is there a ‘perfect’ moment to do that?

When to replace a child safety seat? Division of child safety seats based on toddler’s weight and height

Certain parents consider changing a child safety seat mainly basing on their intuition or on the often misleading observations and conclusions. How to do it right – neither too early nor too late? The weight, height and age criteria according to which the child safety seats are categorised are extremely helpful in this matter. They clearly specify when to replace the seat with a next-group product. It is worth remembering that the weight category is by far the most frequently taken into account – despite the introduction of the i-Size standard which provides the division that also takes into account the height of small passengers.

The seats are divided as follows:

  • infant seats, i.e. carrycots (0/0+ group) – from 40 up to approx. 86 cm, max. 13 kg;
  • toddler seats (I/II group) – up to 105/125 cm, from 9 months to approx. 4/5 years old, from 9 up to 25 kg;
  • seats for older children (II/III group) – from 100 to 150 cm, from 4/5 to approx. 12 years old, from 15 to approx. 36 kg.

Infant car seat (carrycot)

This is the first car seat your child will travel in from birth until 9-12 months of age (depending on weight and height). The child safety seat is fitted with the using either 3-point seat belts or the ISOFIX system, and it is important to remember that both methods provide a similar safety standard as long as the installation is carried out correctly. Infant seats are placed rearward-facing (RWF) to provide maximum protection for the baby.

When to switch from carrycot to child safety seat?

The experts agree that parents should use infant seats for as long as possible, as they provide the baby with the highest comfort level and side protection. Eventually, however, there comes a moment when the child grows out of it. When to replace a 0–13 kg seat?

  1. Exceeding the weight limit, i.e. 13 kg – remember that even 0.5 kg makes a huge difference in this case. Safety tests use dummies weighing up to 13 kg, so there is no way of knowing how such a seat would behave with a child weighing, e.g. 13.5 kg and more.
  2. The height of the child above the acceptable standard, i.e. approx. 86 cm – if you are wondering when to replace the 0–13 kg seat with a larger one, carefully observe how your baby fits in the carrycot. If the head protrudes beyond the upper edge of the backrest, it is absolutely necessary to change the seat.
  3. The harness straps are too short to be comfortable for the baby.

Now, let’s modify the question “when to switch from carrycot to child safety seat” slightly: when is it possible, but not necessary, to replace the 0-13 kg car seat? Well, this is not needed when the legs of your baby protrude from the carrycot and are in free contact with the backrest of the rear seat. This is a normal occurrence in seats designed for infants. The same applies if your child can sit up unaided or hold the head up – it is not necessary to replace the seat with a larger one.

Toddler car seat

This is the second type of seat for your child. Usually it is used up to approx. 4 years of age, however certain manufacturers (e.g. Avionanut) offer seats in this category that may be used even until the age of 6. They are installed with the use of ISOFIX or car seat belts. Depending on the specific model, they can be adapted for rearward or forward-facing placement. It is worth remembering that according to the i-Size standard (ECE-R129), children should travel rearward facing until at least 15 months of age – although this position is usually recommended up to 4 years of age.

When to replace a child safety seat with a larger one?

Replacing such a seat with a larger model should depend on the following criteria:

  1. Weight – max. 18/25 kg. After the limit is exceeded, the seat should be replaced with a larger one adapted to the next weight category.
  2. Height – If you are not sure when to switch to a bigger seat, both the weight and the height of your baby can help you decide. In the I/II group, the seats are usually suitable for children with the height of up to approx. 105 or 125 cm. The range may vary depending on the specific seat model.
  3. The eye level of your child in relation to the headrest of the seat – when their eyes are at the height of the highest point of the headrest, the seat needs to be replaced.
  4. Check the shoulder straps – in general, they cannot come out from under the shoulders (they need to fall straight on them), however, with rear-facing seats this should not be an issue as long as it does not cause inconvenience.

Car seat for older children

This group includes seats used by children from the age of 4-5 until they are about 12 years old – it means even up to 7-8 years of use. Note that this is the only way you can guarantee the best protection for your child, so you are advised to use it for as long as possible. Even if your child does not like travelling in a car safety seat, you should not give in to their pressure and keep the full system instead of replacing it with a booster seat which does not provide the necessary safety in case of sudden road events.

When does the use of a car seat become unnecessary?

  1. Weight criterion – 36 kg (depending on manufacturer guidelines as there are already seats without a weight criterion on the market).
  2. Height criterion – max. 150 cm.
  3. Please read applicable laws in the country of your residence – in Poland, the amendment to the Road Traffic Law annulled the upper age limit (12 years) exempting the children from the obligation to use child car seats. Currently, all children under 150 cm MUST travel in the seat – regardless of age. In practice, it may be mandatory for the parents of a 17/18 year-old to drive their child in a dedicated seat as long as they are under 150 cm in height.

In addition to the above points, it is a good idea to carry out a check to see whether your child is ready to travel without a safety seat. To do that:

  • make sure that your child can sit with their back against the backrest of the rear seat;
  • make sure that they can bend their knees behind the lower edge of the back seat;
  • check the position of the lap belt – whether it is at pelvic level or around the abdomen;
  • check the position of the shoulder strap – whether it fits well, is not too close to the neck, and does not slip off the shoulder;
  • make sure that the child can hold the position and understands your commands – and does not hunch or lean over.

When to replace a child safety seat with a larger one – is there a ‘perfect’ moment to do that?

Spotting the right moment to buy a new seat is not always an easy task and poses a big problem for many parents – fortunately, many manufacturers, including Avionaut, offer car seats with the parameters provided in the smallest detail. This will help you to make a sound decision and choose the right car seat for your child. Visit avionaut.com and see for yourself!

Avionaut Expert
Published: 24.01.2022