How to Choose the Right Size Kids' Clothing Before You Buy
By Shop Kids Clothes & toys | Published: 2026-10-16
Category: Buying Guides
Learn how to measure your child, read size charts, and decide between sizes when buying kids' clothes online. Practical tips for a better fit every time.
Quick answer
Measure your child's chest, waist, and height, then compare those numbers to the brand's size chart—not the age label. When between sizes, size up for tops and pyjamas to allow room for growth and comfort, and choose the smaller size only if the item is meant to be snug or your child is at the top of the current range.
Measure Your Child at Home in Three Steps
You only need a soft tape measure and a few minutes. Have your child stand straight in lightweight clothing or underwear. Measure the chest at the fullest point, the waist at the natural crease (usually just above the belly button), and the height from the top of the head to the floor without shoes. Write these numbers down and note the date—kids grow quickly, so remeasure every two to three months.
Read the Size Chart, Not the Age Tag
Age labels vary widely between brands. A 4T from one label may fit like a 5 from another. Always open the specific product's size chart and match your child's measurements to the chest, waist, and height columns. If your child's measurements fall between two sizes, consider the garment's intended fit. For a relaxed t-shirt like the Tyler Striped short-sleeve T-shirt, the boxy cut and dropped shoulders already provide extra room, so you might stay with the smaller size if your child is on the lower end of the range. For pyjamas, a flexible fit is key—the Wilhelm Grow Striped Pyjamas Set includes a touch of elastane for stretch, so sizing up can extend wear without feeling baggy.
Factor In Fabric and Fit for Different Garments
Fabric affects how a size feels. Organic cotton with a smooth, thick finish (like the Tyler tee) holds its shape and may feel firmer at first, while cotton blended with elastane (like the Wilhelm pyjamas) stretches with movement. For accessories like sun hats, adjustability matters more than a single measurement—the Gorm Reversible Sun Hat and the Gorm Linen Sun Hat both have drawstrings at the back and a bendable brim, so you can fine-tune the fit as your child grows. When buying online, check the product description for any fit notes, such as 'relaxed' or 'snug,' and read a few reviews from parents with similar-sized kids.
Decision rules for sizing kids' clothes online
- When to size up: If your child's measurements are at the top of a size range or between two sizes, choose the larger size for tops, dresses, and pyjamas. This allows room for growth and layering, and prevents the item from being outgrown in weeks. Size up for longevity and comfort in relaxed-fit garments.
- When to stay with the current size: If the garment is designed for a snug fit (e.g., leggings, swimwear) or your child is at the lower end of the range, stick with the smaller size. For relaxed styles like the Tyler tee, the boxy cut already provides extra room. Match the size to the intended fit, not just age.
- When to check adjustability: For accessories like hats, look for adjustable features such as drawstrings or bendable brims. These allow a custom fit even if your child is between sizes or grows quickly. Adjustable accessories can bridge size gaps.
Product facts to know
- Tyler Striped short-sleeve T-shirt - Y/D stripe classic navy sandy: Tyler Striped short-sleeve T-shirt – Y/D stripe classic navy sandy is made from thick organic cotton with a smooth finish, a boxy fit, and dropped shoulders. The relaxed cut gives room to move and layer, so you can often choose your child's current size rather than sizing up.
- Wilhelm Grow Striped Pyjamas Set - Y/D Sandy / Pale tuscany stripe: Wilhelm Grow Striped Pyjamas Set – Y/D Sandy / Pale tuscany stripe is crafted from soft, breathable organic cotton with a touch of elastane for a flexible fit. The stretchy fabric accommodates growth spurts and movement during sleep, making it a good candidate for sizing up if your child is between sizes.
- Gorm Reversible Sun Hat - Sailing / Sandy: Gorm Reversible Sun Hat – Sailing / Sandy is made from 100% GOTS-certified organic cotton and features a soft, bendable brim, drawstrings at the back, and a longer neck flap. The adjustable drawstring and bendable brim let you customize the fit, so you can get a secure, comfortable hat even if your child is between age ranges.
Fit guidance for common kids' clothing
Best for
- Parents buying online who want to minimize returns
- Children who are between sizes or growing quickly
Not for
- Those looking for a one-size-fits-all solution without measuring
- Buyers who prefer to try on in-store before purchasing
