Baby & Kids Clothing Size Guide for Canada: Ages, Brands & Conversions (2026)

In this baby and kids clothing size guide, we get straight to the point: sizes vary from brand to brand by one to two sizes, especially between European brands (Petit Bateau, Jacadi, Boboli) and North American ones (Carters, Pekkle, Souris Mini). To avoid mistakes, go by measurements in centimetres, not by the age printed on the tag.

 

We see it in our Montreal boutique every day: a parent holds two "12 months" sweaters in their hands, one Jacadi, one Pekkle, and the difference is obvious at a glance. This baby and kids clothing size guide is here to help you avoid that kind of surprise — whether you're shopping new, shopping secondhand, or trying to fit a gift an aunt brought back from Paris.

How to choose baby clothing sizes (0–24 months)

Why the age on the tag often lies

Age is a statistical average, not a truth about your baby. According to the growth curves published by the Public Health Agency of Canada, an "average" 6-month-old measures roughly 67 cm (26 in) and weighs 7.5 kg (16.5 lb). But your baby could easily measure 70 cm at 4 months, or 65 cm at 8 months. Serious brands always show a height and weight range alongside the age. That range is what matters.

The simple rule: measure, don't guess. A $2 fabric tape saves you $30 in wrong-size purchases.

The three systems you'll run into in Canada

In Canada — and especially in Quebec — you're juggling three baby size systems at once:

• The French system (FR): a number equal to height in centimetres. A 74 = 74 cm. Used by Petit Bateau, Jacadi, Obaïbi, Boboli.
• The North American system (US): an age in months (3M, 6M, 12M, 18M, 24M). Used by Carters, Pekkle, Gap, Old Navy, and most Canadian brands.
• The years system: takes over after 24 months (2T, 3T, 4… up to 14).

Because we stock all three on the same shelves, we've learned to translate everything into centimetres. It's the only reference that doesn't lie.

Size chart: 0 to 24 months

Age	FR size	US size	Height (cm)	Height (in)	Weight (kg / lb)
Newborn	50	NB	46–50	18–20	3–4 / 6.6–8.8
1 month	54	0–3M	51–54	20–21	4–5 / 8.8–11
3 months	60	3M	55–60	22–24	5–6 / 11–13
6 months	67	6M	61–67	24–26	6–8 / 13–18
9 months	71	9M	68–71	27–28	8–9 / 18–20
12 months	74	12M	72–74	28–29	9–10 / 20–22
18 months	81	18M	75–81	30–32	10–11 / 22–24
24 months	86	24M	82–86	32–34	11–12.5 / 24–28

Size at birth: 0M, 1M, or 3M?

A classic hospital-bag question. For a full-term baby of average weight (3 to 3.5 kg / 6.6–7.7 lb), the newborn size is only worn for 2 to 3 weeks. The 1-month size (or 0–3M) covers the first 4 to 6 weeks. Our honest advice: buy 2 to 3 newborn pieces (pyjamas, onesies), and focus on 1-month and 3-month sizes for everything else. Buying secondhand, you'll find newborn pyjamas in like-new condition at our store for $4 to $6, because babies only wore them for a few days.

For preemies, we have a dedicated section in partnership with Prema Québec — rare in Canada, and parents regularly tell us it's a relief.

Kids sizes 2 to 10: the real puzzle

After 24 months, a kids clothing size guide in Canada gets significantly trickier: we switch from months to years, brands introduce half-sizes, and growth slows down but becomes less predictable. This is the age where we see the most confused parents in our Saint-Hubert boutique.

Size chart: 2 to 10 years

Age	FR size	US size	Height (cm)	Chest (cm)
2 years	86	2T	82–88	52
3 years	94	3T / 3	89–96	54
4 years	102	4T / 4	97–104	56
5 years	108	5	105–112	58
6 years	114	6	113–118	60
7 years	120	7	119–124	62
8 years	126	8	125–130	64
9 years	132	9	131–136	66
10 years	138	10	137–142	68

Why a "4 years" isn't always a "4 years"

A Petit Bateau "4 years" = 102 cm in height. A Carters "4T" = roughly 99–104 cm, but cut more generously at the belly and sleeves. A Souris Mini "4" = often wider in the shoulders. Three brands, three realities. The number on the tag tells you almost nothing without its matching measurement.

Converting baby clothing sizes: Europe to North America at a glance

Quebec is one of the rare North American markets where both systems really coexist. If you buy a spring outfit from a French aunt's trip back home, or a pyjama from Souris Mini for back-to-school, you're jumping from one system to the other without noticing.

Quick conversion chart

Height (cm)	FR size	US size (baby)	UK size
50	50	NB	Newborn
60	60	3M	0–3m
67	67	6M	3–6m
74	74	12M	9–12m
86	86	24M / 2T	18–24m
94	94	3T	2–3y
102	102	4T	3–4y
114	114	6	5–6y
126	126	8	7–8y

The 5-second rule

If you're looking at a European tag and you're used to shopping in months: take the cm size and do the mental math. 74 cm ≈ a North American 12M. 86 cm ≈ 24 months. 94 cm ≈ 3 years. This shortcut covers 90 % of cases.

The reverse is trickier: some North American brands run generous. A Carters 2T can easily fit a child of 94–96 cm that a French tag would classify as 3 years. That's why the next section matters.

Size differences between brands (what we notice in the boutique)

We see thousands of items pass through every month. Over time, you get to know each brand like a neighbour — its strengths, its quirks, its surprises. Here's what we observe on the brands we stock the most.

Petit Bateau — true to size, occasionally small

The gold standard. Sizes match height in cm, period (this is the official Petit Bateau convention, explained on the Petit Bateau website). But the cuts are narrow at the shoulders and sleeves, especially on ribbed bodysuits and t-shirts. If your child is broad across the upper body, size up. Petit Bateau's stitching is famously durable — their pieces easily survive three children, which is why we usually have them in stock around $6 to $10.

Jacadi — classic European cut

Height in cm, same as Petit Bateau. Sleeves run slightly longer, fitted cut — ideal for slim, long-limbed kids. Jacadi dresses and rompers are notoriously beautiful to resell because they don't go out of style.

Souris Mini — Quebec brand, generous cut

North American sizes, but roomier than Carters. A Souris Mini "4" usually fits like a Petit Bateau "4 years", but with more belly room. Perfect for kids between two sizes who need a bit of breathing room.

Petit Lem — Montreal, standard fit

Consistent NA sizes. Petit Lem's organic cotton pyjamas are one of the fastest-moving items we resell. True to size, rarely a surprise.

Perlimpinpin — soft, not always to label

Another Quebec brand. Their onesies and sleep sacks sometimes run big, especially in newborn sizes. We often see a Perlimpinpin "3 months" worn comfortably up to 4 or 5 months.

Boboli — Spain, broad shoulders

Sizes in cm. Cuts are wider than Petit Bateau, especially in the chest. If your child is built on the sturdier side, Boboli is forgiving. Bright colours, very popular in spring.

Jan&Jul, Caribou, Stonz — outerwear, measure twice

Outerwear brands. Their jackets and snowsuits run intentionally big to leave room for base layers. Never size UP on a kids winter jacket "so they can grow into it" — it'll be too big all winter, then too small before the next season.

How to measure your baby or child properly

The four measurements that actually matter:

1. Height (standing, feet flat, against a wall). The most important measurement for bodysuits, sweaters, pants, dresses.
2. Chest (at the widest point, under the arms). Useful for jackets, shirts, dresses.
3. Waist (where your child naturally bends). For pants and skirts.
4. Inseam (from the groin crease to the ankle). For pants and rompers.

Jot these four numbers into a note on your phone. Update them every 2 to 3 months before age 2, every 6 months after. You just eliminated 80 % of return problems.

The secondhand trick: measure a garment, not a child

A wriggling child is hard to measure. Our pro tip: take a piece of clothing that fits your child perfectly, lay it flat, and measure it. Shoulder width, total length, sleeve length, inseam. Compare those numbers to the pieces you want to buy. It's the most reliable method for secondhand shopping, and it's exactly what our size calculator uses behind the scenes.

When to move up a size

The concrete signs that don't lie:

• Sleeves ride up above the wrists when arms are extended.
• The belly pokes out when your child raises their arms (a bodysuit that "unsnaps").
• The bottom is tight on pants or overalls.
• The foot is cramped in footed pyjamas.
• Shoulders are bursting, sometimes literally, especially on Petit Bateau.

The classic mistake we see in parents: holding onto a size too long "because it still fits". If your baby has red marks on their thighs when you take off their onesie, it's been too small for two weeks.

Typical size-change pace (non-linear)

• 0–6 months: new size every 4 to 6 weeks.
• 6–12 months: every 2 to 3 months.
• 12–24 months: every 3 to 4 months.
• 2–5 years: every 6 to 9 months, sometimes longer.
• 5 years and up: roughly one size per year, sometimes a half-size.

The silver lining: this is exactly why secondhand makes so much sense at this age. A Petit Lem pyjama at $6, worn for 4 months, works out to $1.50 per month of wear. Good luck hitting that ratio buying new.

Buying secondhand: choosing the right size without a fitting room

This is the big fear for parents new to online secondhand baby shopping. No fitting room, no way to return a onesie that doesn't quite work. Here's the method we recommend to our customers:

1. Know your child's measurements (height, chest, waist). Not age — measurements.
2. Adjust by brand. Petit Bateau? True to size. Carters? Size down half a size. Souris Mini? Size up a half if your child is between two sizes.
3. Read the condition description. At our store, every piece is graded: new with tags, like-new, excellent, good. "Good" on a pair of jeans is normal. "Good" on a newborn pyjama is suspicious.
4. Plan for the winter layer if you're shopping in the fall for winter. A mid-season sweater should have enough room for a cotton base layer underneath by January.
5. Start with the age-based collections to filter fast: babies 0–24 months or kids 2 and up.

A concrete example we see often: a customer orders a bundle of six Petit Bateau "6 months" bodysuits for her son who wears Carters "6 months". The bodysuits arrive — too small. It's not a curation problem; it's the cut gap between the two brands. If she'd picked a 74 (French "12 months") instead, everything would have fit. Learn this rule once, save years of mistakes.

Sizes and Canadian winters: think in layers

In winter, a child in Canada rarely wears just one layer. A long-sleeve top, a thick sweater, a jacket, a hat, mittens — and underneath, often a thermal base layer. When you pick a size for a jacket or snowsuit, think about what goes underneath.

Outer jacket: true to size, even slightly fitted. A jacket that's too big loses heat (air circulates too much) and restricts movement. Leave just enough room for a fleece.

Snowsuit: go by current height. Outerwear pieces are already designed roomy.

Winter boots: the one item where you don't "size up to grow into it". A boot that's too big means the foot slides = blisters + cold. Go true to size, even if it means rebuying mid-season. Browse our kids footwear.

Our seasonal checklist breaks all this down by month and age, so you're never caught off guard by the first snowfall.

Frequently asked questions

What size is a Petit Bateau "3 months"?

At Petit Bateau, sizes follow height in centimetres. The "3 months" corresponds to a 60 (about 55 to 60 cm in height, and 5 to 6 kg in weight). That's often equivalent to a "newborn" or "0–3M" at North American brands. If your baby is 62 cm at 3 months, skip straight to the 67 (French "6 months").

How do I convert an 18M size to a French size?

An 18M North American size corresponds roughly to a French 81 (about 78 to 81 cm in height). It's also often equivalent to the "2 years" at several European brands, because cut conventions shift at 24 months. If your child wears 18M and you're eyeing a Jacadi dress, aim for the 81.

What's the difference between 24 months and 2 years?

In theory, they're the same size — both cover roughly 82 to 88 cm. In practice, "24 months" pieces are often cut like baby clothing (roomier, wider necklines so they fit over the head), while "2 years / 2T" pieces are cut like toddler clothing (defined waist, no snap crotch).

My baby is between two sizes — which do I pick?

Pick the larger one, except for footed pyjamas and bodysuits where a too-large size slides off the shoulders. For pants, overalls, and dresses, sizing up leaves room for another 2 to 3 months of wear. And remember: buying secondhand at $5 or $8 per piece, the margin for error is much more forgiving than buying new at $35.

How do I know if a secondhand item will fit without trying it on?

Two methods: (1) cross-reference the actual measurements of the item with a garment that already fits your child, or (2) use our kids clothing size calculator, which compares your measurements to brand-by-brand charts. The base rule: height in cm never lies.

Are newborn sizes worth buying?

Yes for 2 to 3 pyjamas and onesies — no for a full wardrobe. An average baby outgrows newborn in 2 to 3 weeks. Buying secondhand, it's THE size where you find the best like-new pieces, because they were only worn a handful of times. Our baby pyjamas 0–24 months prove the point.

Final word

This entire baby and kids clothing size guide comes down to three habits: measure your child, learn two or three brands you love, and never trust the age on the tag. Add secondhand to the equation, and the financial risk becomes negligible — you can get it wrong once without regretting it.

Ready to try the method? Our calculator at the top of the page handles the conversion work for you, and our age-based collections (0–24 months and 2 and up) are sorted so a height in cm lines up with a real size range, not a marketing label. And if you're passing through Montreal, the Saint-Hubert boutique is still the fastest place to learn a brand — hold three "2 years" side by side, and in 10 seconds you understand everything this guide explains.