How to Buy Baby Clothes and Pajamas Online: Sizes, Snug Fit and Fabrics (What to Check)

Baby clothes look simple online, but sizes vary between brands, children grow quickly and sleepwear has its own safety rules. Ordering the wrong size or fabric is common, and many baby stores limit returns to unworn, unwashed items with tags. This guide covers how to choose sizes, what the fabric labels mean, the US rules on children's sleepwear and the policies to read before you buy for your own child or as a gift.

Size by weight and height, not age

The age on a label is only a rough guide. Most brands publish a size chart with weight and height ranges, and those numbers are more reliable:

• Weigh and measure the baby, then pick the size whose range they fall in, not the one that matches their age in months.
• If your child is near the top of a range, or in a high percentile, size up.
• Check whether the chart allows room for cloth or disposable diapers.
• Babies often move through newborn and 0–3 month sizes within weeks, so buy fewer of the smallest sizes.
• For gifts, choose a size or two ahead of the baby's current age, and think about the season they will be wearing it in.

Sizes are not standardized across brands. One label's 6–9 months can fit like another's 3–6 months, and European brands often size by height in centimeters, such as 68 or 74. If you already have a piece that fits well, lay it flat and measure chest width and length, then compare those numbers with the measurements on the product page where they are given. Reviews that mention whether a style runs small or large are also worth reading, especially for sleepers with feet, which can become too short in the leg before the body is outgrown.

Understand children's sleepwear rules

In the US, the Consumer Product Safety Commission requires children's sleepwear in sizes above 9 months to be either flame resistant or snug-fitting. That is why many cotton pajamas are cut close to the body and carry a yellow hang tag saying "wear snug-fitting, not flame resistant." Garments sized 9 months and under are exempt.

• Do not size up cotton pajamas just for a roomier fit, since a loose cotton pajama no longer meets the snug-fit standard.
• Loose-fitting sleepwear such as fleece or nightgowns in larger sizes should be labeled flame resistant. If the listing does not say, check the label or ask.
• Follow safe sleep guidance for babies: no loose blankets in the crib, and use a wearable blanket or sleep sack instead.

Read the fabric line

The fabric content tells you more than words like soft or natural:

• Organic cotton is cotton grown without synthetic pesticides. The GOTS label (Global Organic Textile Standard) certifies both the fiber and how the fabric is processed, including dyes and chemicals.
• Cotton with spandex stretches and holds its shape better, which helps snug-fit pajamas.
• Lyocell or TENCEL blends are smooth and drape well, and feel cooler.
• Fleece is usually polyester, sometimes recycled. It is warm but less breathable.
• OEKO-TEX certification means the finished fabric was tested for harmful substances, which is different from being organic.

Babies with eczema or sensitive skin often do better in plain cotton with fewer synthetic blends and no heavy prints on the inside.

Look at the practical features

• Two-way zippers make night-time diaper changes faster.
• Zipper guards at the chin stop the zip from rubbing.
• Fold-over mittens on newborn sizes help prevent scratching.
• Non-slip grips on footed sleepers matter once a baby starts to walk.
• Snaps versus zippers is a personal preference, but many parents find zippers faster.

Think about the season and how your baby will sleep. Lightweight cotton suits warm rooms and summer, while thermal, waffle-knit or fleece layers suit colder nights. Wearable blankets and sleep sacks are often rated by TOG, a measure of warmth: lower numbers for warm rooms, higher for cool ones. Dress the baby for the room temperature rather than piling on layers, and check the back of the neck to see whether they are too hot or cold.

Check shipping and return terms before you order

Baby stores often have stricter terms than general clothing shops:

• Condition: returns usually need items unworn and unwashed, with tags. Try sizes before washing.
• Fees: some brands deduct a handling fee or sell optional return coverage at checkout.
• Exchanges: not all stores offer them, which means returning and reordering.
• Final sale: clearance, gift sets and seasonal items are frequently non-returnable.
• Shipping: free-shipping thresholds may exclude Alaska, Hawaii, military addresses and territories, and standard delivery can take up to two weeks, so order early for holidays or a baby shower.

For a worked example of a US organic baby clothing store, including its size chart and return fees, see our Burt's Bees Baby review.

Wash and care to make clothes last

Wash new baby clothes before first wear, but only once you are sure the size is right. Use a mild, fragrance-free detergent, wash cotton cold or warm, and tumble dry low or line dry to limit shrinkage. Close zippers before washing to protect the fabric, and follow the care label on flame-resistant sleepwear, since some labels advise against fabric softener.

A quick checklist

• Weight and height checked against the brand's own size chart
• Snug-fit or flame-resistant labeling on sleepwear above 9 months
• Fabric content, and GOTS or OEKO-TEX certification if that matters to you
• Zippers, mittens and foot grips that suit your baby's age
• Return window, condition rules, fees and whether exchanges are offered
• Final sale status on clearance and gift sets
• Free-shipping threshold and delivery time for your address