The biggest reason parents hesitate on secondhand kids' clothing isn't price or condition, it's sizing. A "24 months" label from one brand can fit like an 18-month from another, and a child's actual measurements rarely line up perfectly with the number on the tag anyway. When you're buying in person, that's a quick problem to solve, you hold it up, maybe try it on. When you're buying from a listing photo on a secondhand site, you don't get that chance.
The good news is that sizing secondhand accurately is a skill, not a guessing game, and it gets much easier once you know what to actually look for.
Measure your child, not the tag
Clothing size labels are a rough guide at best, they vary between brands, between countries, and even between seasons within the same brand. The more reliable approach is to measure your child directly and compare those measurements to the specific garment, not just the size printed on it.
Two measurements matter most for kids' clothing:
- Height, measured standing against a wall, which most size charts are built around
- Chest or torso width, measured under the arms, which matters more than height for how snug something like a onesie or jacket will actually fit
Write these down and keep them somewhere handy, they'll stay useful for weeks or months depending on your child's age and growth pace.
Read the listing for actual measurements, not just the size
A well-written secondhand listing will often include garment measurements, laid flat, not just a size label. This is the single most useful piece of information a seller can give you, because it sidesteps the brand-to-brand inconsistency entirely.
If a listing doesn't include measurements, it's completely reasonable to ask the seller directly, most are happy to grab a tape measure for a specific item. If a shop or seller consistently doesn't provide this, that's worth factoring into whether you buy from them regularly.
Know which categories run generous or small
A few patterns hold fairly consistently across secondhand kids' clothing, worth keeping in mind as general tendencies rather than hard rules:
- Outerwear (snowsuits, jackets) is often sized to allow room for bulky layers underneath, so it can run generous. Buying slightly ahead of your child's current size is usually safe here.
- Footwear has almost no forgiveness, a half size off matters much more for shoes than for a shirt. If a listing doesn't give an insole length in centimetres, ask for one before buying secondhand shoes.
- European and North American sizing use different systems entirely, a European size 92 is roughly equivalent to an 18-24 month North American size, but "roughly" is doing real work in that sentence, so check a conversion chart rather than assuming.
Buy slightly ahead when the price makes sense
Kids grow fast enough that buying one size ahead of where they currently measure is often a reasonable bet, especially for secondhand items where the cost of being slightly wrong is much lower than buying new. If a snowsuit is priced well and sits at the upper edge of what your child's current measurements suggest, it's often worth it, since they'll likely grow into it within the season rather than out of it.
When in doubt, ask before you buy
Most sellers on secondhand platforms are parents themselves, and most are genuinely happy to answer a quick question about fit before you commit. A short message asking for a specific measurement, or how a similar-aged child fit the item, usually gets a fast and helpful answer. It's a much better use of five minutes than receiving something that doesn't work and having to resell it yourself.