Children's Pajamas: How to Choose Sleepwear for Warmth, Fit and Safety
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Pajamas get less thought than almost anything else in a child's wardrobe. They are bought in multipacks, passed down without a second look, and worn until the knees go. Yet they are the clothes your child spends the most hours in, and the only ones they wear while you are not watching.
Getting them right comes down to three questions: is this warm enough for the room, does it fit the way sleepwear should, and is it in good enough condition to do the job. Here is how to answer each one.
Start With the Room, Not the Child
The most useful tool for choosing sleepwear is not a size chart. It is a room thermometer.
The Lullaby Trust, the UK's safer sleep charity, recommends keeping a baby's room between 16 and 20°C. Most parenting guidance builds from that range: once you know the temperature of the room, you can choose layers to match it, rather than guessing from what the weather is doing outside.
The common mistake is overdressing. Babies regulate temperature less well than older children, and a warm, heavy layer plus a thick sleeping bag plus a heated room adds up quickly. The reliable check is to feel your baby's chest or the back of their neck. Hands and feet are usually cooler and tell you very little. Warm is fine. Sweaty or clammy means a layer should come off.
Sleeping Bags and Tog Ratings, Explained
For babies and young toddlers, a sleeping bag usually does the work a duvet would do for an adult. Safer sleep guidance favours them because they cannot be kicked off or pulled over the face.
Sleeping bags are rated in tog, a measure of how much warmth the fabric holds. The higher the number, the warmer the bag. As a broad guide used across UK and European brands:
| Room temperature | Typical sleeping bag | What usually goes underneath |
|---|---|---|
| Below 16°C | 2.5 tog | Sleepsuit plus a bodysuit |
| 16–20°C | 2.5 tog | Sleepsuit or footed pajamas |
| 20–22°C | 1 tog | Sleepsuit |
| 22–24°C | 0.5–1 tog, or none | Light sleepsuit |
| Above 24°C | 0.5 tog or none | Bodysuit only |
Treat this as a starting point and always follow the chart that comes with the specific bag. Two further rules matter as much as the tog:
- Fit matters more than size label. A sleeping bag that is too big lets a baby slip down inside it. The neck and armholes should be snug enough that their head cannot pass through.
- No hats indoors for sleep. Babies lose heat through their heads, and covering it is one of the simplest ways to overheat. Our hats, mittens and scarves guide covers what to wear outdoors; at bedtime, the head stays bare.
Which Fabric for Which Nights
Children's sleepwear is made in four main fabrics, and each suits a different kind of night.
Cotton jersey. The everyday default. Breathable, soft, and easy to layer under a sleeping bag. Best for heated homes and for children who run hot.
Velour. The French nursery classic, and the fabric you will see most often from Petit Bateau, Absorba and Moulin Roty. Velour has a short, dense pile that holds warmth without bulk. It is ideal for babies in cooler rooms, especially as a sleepsuit inside a sleeping bag.
Fleece and brushed cotton. The warmest option, best kept for genuinely cold rooms or older children who have moved out of a sleeping bag and kick off their covers. On a child who already runs warm, fleece can be too much.
Ribbed cotton. Close-fitting and stretchy, ribbed pajamas move with a restless sleeper and stay put. They are often sold for toddlers who are moving into a bed for the first time.
A good rule across all of them: as children get older and sleep under a duvet, the pajamas themselves can get lighter, because the bedding is doing more of the warming.
Close Fit Is a Feature, Not a Flaw
Pajamas are meant to fit closer than daywear. Fitted sleepwear stays in place, does not bunch around a child's neck or ride up under bedding, and leaves less loose fabric to catch on anything.
In Europe, children's nightwear is assessed against a dedicated flammability standard, EN 14878, which covers pajamas and other nightwear for children up to 14. Close fit and fabric choice are part of how manufacturers meet it. For parents, the practical takeaways are simple: choose sleepwear that is actually sold as sleepwear, and avoid putting children to bed in loose, floaty daytime pieces.
Sizing Pajamas by Brand
The same brand habits we cover in our fit guide apply to sleepwear, and in some cases they are more pronounced, because pajamas are cut close by design.
- Petit Bateau runs smallest. Its pajamas and sleepsuits are snug from the start, so size up, particularly on footed styles.
- Jacadi is slim and height-based. If your child is between sizes, take the larger one.
- Hatley, Tea Collection and Crewcuts use American sizing, which is roomier in the body. Take your child's age size.
- Footed pajamas and sleepsuits are usually outgrown at the feet before anywhere else. If toes are pressing against the end, or the fabric pulls tight from shoulder to foot when your child stretches, it is time for the next size even if the width still fits. Some Petit Bateau sleepsuits are made 2-in-1, with fold-over or removable feet, which buys extra weeks.
If you are unsure how European height-based sizes map to age, our EU, UK and US size guide has the full conversion table.
How many pairs? Most families find three to four pairs per size covers a week comfortably, allowing for one in the wash and one spare for the night-time change that always happens eventually.
What to Check on Pre-Loved Sleepwear
Pajamas are one of the best categories to buy pre-loved. Children usually outgrow them long before they wear out, and the softness parents love only improves with washing. A few checks are worth making on any piece:
- Poppers and zips. Every snap should close firmly and release cleanly. Zips should run smoothly, with an intact guard at the top so metal does not sit against the chin.
- Cuffs and elastic. Ankle and wrist cuffs should still spring back. Tired elastic lets legs ride up overnight.
- Seams at the crotch and underarm. These take the most strain from kicking and stretching.
- Velour pile. Some flattening on the seat and knees is normal. Bald patches mean the fabric has lost much of its warmth.
- Feet and grips. On footed styles, check soles for thinning, and check any non-slip dots are still attached.
- No added cords or loose trims. Ribbons, pompoms and drawstrings have no place on children's nightwear.
Every piece in our shop is inspected for exactly these points and given a clear condition grade, so you know what you are getting before it arrives. For keeping sleepwear soft through repeated washing, our guide to making children's clothes last longer covers temperatures, drying and storage.
Frequently Asked Questions
What should a baby wear to bed in a 18°C room? A sleepsuit or footed pajamas inside a 2.5 tog sleeping bag is the usual combination at 16–20°C. Check your baby's chest or the back of their neck, and remove a layer if they feel sweaty.
Are velour pajamas warmer than cotton? Yes. Velour's dense pile holds more warmth than flat cotton jersey of the same weight, which is why it is so popular for babies in cooler bedrooms.
When should my child stop using a sleeping bag? Many children move out of a sleeping bag when they move into a bed, often between two and three years old. At that point, warmer pajamas and a properly fitted duvet take over.
Do pajamas shrink? Most shrinkage happens in a garment's first few washes. Pre-loved pajamas have already been through those, so the size you see is the size you get.
Is it safe to buy pre-loved pajamas? Yes, provided they are in good condition: secure fastenings, intact seams, working elastic and no added cords or trims. Those are exactly the points we check before any piece is listed.
Find the next size in sleepwear across Petit Bateau and every label in Brands We Love. And when this size is outgrown, our Sellback program turns it into credit toward the next.