Osteopathy and Childhood: What Are the Benefits for Supporting Your Child’s Development?
July 5, 2026
The first years of life are an extraordinary time of discovery, learning, and change.
Baby onesies are the most commonly worn item of clothing during the first few months of life. Every baby has several of them—but choosing the right one means understanding the differences in style, material, closure, and size. This comprehensive guide will help you dress your baby wisely from birth to 18 months. 🐸
A onesie (also known as baby pajamas, a sleep suit, or a sleepsuit) is a one-piece garment that covers a baby’s entire body, from the feet to the neck. It differs from a bodysuit in that it has long legs with built-in feet. It is the go-to sleepwear for infants and babies up to 18–24 months.
The most common style: it covers the entire body, including the feet. Ideal for nighttime use because it keeps the baby from kicking off the blanket. The non-slip feet are very useful as soon as the baby starts to stand up.
A much-appreciated innovation: a zipper that opens on both sides. For nighttime diaper changes, opening just the bottom part means you don’t have to undress the baby completely—which is essential for not waking the baby up fully at 3 a.m.
It's more versatile, allowing you to add slippers depending on the temperature. Great for summer or as an everyday outfit.
Magnetic closures make dressing your baby quiet and super-fast, even in the dark. Perfect for parents who change their baby at night without turning on the light.
The gold standard for infants' delicate skin. Gentle, breathable, hypoallergenic, and free of chemical residues. The top choice for sensitive skin.
A thicker and softer knit than standard jersey. Slightly warmer—ideal for transitional seasons. Withstands repeated washings.
For winter nights: provides superior warmth. Pair with a TOG- sleeping bag e suited to the room temperature.
Ultra-soft, temperature-regulating, antibacterial. Especially recommended for babies who sweat easily or have skin prone to eczema.
Onesies often run slightly small—the built-in feet limit how long they can be worn. If in doubt, always choose the next size up.
The onesie shouldn't be used on its own in cool weather—it should be paired with a sleeping bag. The idea is to use a lightweight onesie plus a sleeping bag that's appropriate for the season's TOG rating. Never use a blanket on top before 12 months of age.
Before 18 months, a onesie is recommended: it doesn’t ride up or slip down during the night. With two-piece pajamas, there’s a risk that the top will ride up and expose the baby’s tummy. A onesie provides even coverage over the entire body, which pediatricians recommend to prevent the baby from getting cold at night.
Starting at 18–24 months, when the child is more independent and begins to undress on their own, two-piece pajamas can gradually take over.
Plan on buying 5 to 7 onesies per size. Nighttime accidents (spit-up, diaper leaks) often mean you’ll need to change your baby during the night. With 6 onesies, you’ll have plenty of spares even if it takes a day to wash them. Focus your purchases on the 3-month and 6-month sizes—the newborn size is only worn for a very short time.
A well-cared-for organic cotton onesie can be passed down to two or three children. That’s one more reason to invest in quality rather than quantity.
To dress your baby in a coordinated way, check out our guide to baby " bodysuit " —the essential base layer worn under a onesie on cool days—and our tips for dressing your baby in the summer.
Yes, especially during the first few months. Rompers aren’t just for nighttime—many parents dress their infants in rompers all day long. Starting at 3–4 months, you can mix things up more with daytime outfits (bodysuit s + pants, playsuits).
Par temps frais (chambre < 20°C) : oui, un body manches courtes ou longues ajoute une couche de chaleur. Par temps chaud (chambre > 22°C) : la grenouillère seule suffit.
No, as long as the size is right. A onesie that’s too short and pulls on the feet can interfere with hip development. Always make sure there’s enough room for the feet and that the crotch isn’t too tight.
The two complement each other. The onesie is the nightwear. The sleep sack (or sleeping bag) is the blanket used. Together, they make up the ideal nighttime outfit according to French pediatric recommendations.
Soft cotton onesies, double-zip styles, adorable designs, and OEKO-TEX-certified fabrics: PetitMaxou offers a comfortable and practical selection for your baby’s first few months. Free shipping throughout the EU; returns accepted within 14 days.
→ See all onesies and baby clothes PetitMaxou
A set of 3 to 5 organic cotton onesies in a pretty box is one of the most appreciated baby gifts —useful right away, used every day, and often overlooked by expectant parents who focus on the big-ticket items (stroller, crib). If you’re looking for other ideas to round out your gift, our selection of unique baby gifts is a great source of inspiration. Choose size 3 months instead of newborn—the newborn size is worn for only a very short time and is often already given as a set of three.
The first years of life are an extraordinary time of discovery, learning, and change.
Baby sunscreen is one of the summer essentials for new parents —