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When can my child move from a car seat to a booster under 3 months?

A 3-month-old should never be in a booster seat. Booster seats are only for children who have outgrown a forward-facing harness seat, weigh at least 18 kg (40 lb), and are usually at least 4 years old. A 3-month-old must ride rear-facing.

Canadian guidelines set clear weight and age thresholds for each car seat stage, and infants are always at the very first, rear-facing stage.

Strength of evidence

Strong

This is based on Transport Canada's federal safety regulations and a Canadian Paediatric Society clinical guideline, both of which agree closely, making the recommendation clear and well-established rather than based on a single study.

What the evidence says

There is no situation where a 3-month-old baby should be in a booster seat. Booster seats are the third of four car seat stages, and they are only meant for children who are much bigger and older.

According to Transport Canada, booster seats are designed for children who have already outgrown a forward-facing car seat with a harness, and who weigh at least 18 kilograms, which is about 40 pounds. The Canadian Paediatric Society adds that a child should also be at least 4 years old before moving to a booster.

A baby who is only 3 months old is far too small and young for any of this. Babies this age must ride in a rear-facing car seat, which is the very first stage. Rear-facing seats protect a baby's head, neck and spine much better than any other position in a crash.

Your baby should stay rear-facing well past 3 months old. Canadian guidance says babies are safest rear-facing until they are 2, 3, or even 4 years old, as long as they still fit the seat's height and weight limits. There is no need to rush to the next stage.

If you are unsure whether your baby's current seat still fits properly, a local car seat clinic can check the installation and fit for free in many communities.

Sources

✓Reviewed by CH, MD, FRCPC

Reviewed by a specialist physician certified by the Royal College of Physicians and Surgeons of Canada, who has read this answer against the sources listed above and confirmed it reflects them. That is not medical advice about your child. How we review

Answer checked September 4, 2026

Educational information only. Not medical advice, not a diagnosis, and no doctor-patient relationship is created by using this. Founded Parent has not examined your child and does not know their history, so this may not apply to you. In an emergency, call your local emergency number. What Founded Parent cannot do

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