A set of thermal base layers for kids is a brilliant versatile addition to their winter wardrobe. Designed to work best as a cosy layer of insulation against the skin, they should also be breathable to wick away sweat when doing anything active.
Not just designed for skiing and playing in the snow, these tops and bottoms also come in on handy on chilly days out and about, and by their very nature are comfortable and easy to wear.
While base layer sets no doubt come into their own in winter, they’re also useful at other times of the year – particularly if made from merino wool, which works really well to keep your body at an even temperature, whatever the weather.
Merino is also naturally anti-odour, antibacterial and non-allergenic, so it’s a sensible choice if allergies are an issue.
All these featured here are thin enough to be layered up for cold days, but they’re also cosy enough to double as comfortable pyjamas, and some are stylish enough in their own right to be worn alone.
We tested these by wearing them in a variety of indoor and outdoor temperatures, and while doing everything from running around and playing in the park to snuggling on the sofa.
You can trust our independent reviews. We may earn commission from some of the retailers, but we never allow this to influence selections, which are formed from real-world testing and expert advice. This revenue helps to fund journalism across The Independent.
Polarn O. Pyret Nordic Thermal Merino Kids Top & Leggings
Our pick of this cosy bunch, this set from Polarn O.Pyret is the perfect mix of good looks, warmth and value. The Nordic styling is very chic (and also forgiving on food stains etc), and the 100% merino wool and the Fairisle weave style (giving a thicker finish, but not too thick to be overly bulky) take care of the warmth. Flatlock seams mean there are no itchy bits, the top has a dipped back hem to help keep the draughts out, and they work well at regulating warm or cold bodies. And they’re versatile too, equally suited to being a pair of pyjamas as they are under other layers on a cold day out and about.
Available from size 1-2y to 6-8y.
Buy now £61.00, Polarn O. Pyret
Kuling Pink Wool Long Sleeve Shirt and Trousers
Brilliantly simple but effective and lightweight base layers, this set from Kuling offers plenty of breathable warmth – our young tester loved wearing them as pyjamas, and they’re thin enough to layer up easily under mid and outer layers without turning into the Michelin man. They can be washed at 30º but are happiest dried flat. Unlike some others here, neither the top nor the bottom has elasticated cuffs – it’s a personal preference, but some kids don’t like the feel of a tight cuff, and they have flatlock seams for comfort.
Available from size 86/92cm to 146/152cm.
Buy now £36.80, AlexandAlexa
Mini Rodini Viola Wool Shirt and Leggings
Wonderfully vibrant, this matching set from Mini Rodini is made from seriously soft organic merino wool. Properly comfortable, we love the wide collar and the relaxed wide hems at the cuffs, plus flatlock seams throughout. Mini Rodini is rightly proud of its Global Organic Textile Standard certification, meaning its merino wool is produced to the highest standards (including working conditions and chemical use) so we can buy it with confidence. And as a nice matching addition, this set is also available in adult sizes for women.
Available in sizes from 56/62cm to 140/146cm.
Buy now £95.00, Mini Rodini
Smartwool Kids’ Merino 250 Baselayer Crew Top
New to Europe for this winter, Smartwool’s kids’ base layer is the same as the grown-ups’, but just scaled down. The 250 is the heaviest and warmest of the range, designed for use in the coldest of conditions – this is definitely the one to pack for the slopes. Wide hems, flatlock seams and 100% merino wool make it really comfortable to wear and we love the little details, such as the subtle elastic hook on the inside neck.
Available in pink or black, and from size XXS to XL (from approx 100cm to 152cm).
Buy now £51.95, AlpineTrek
Muddy Puddles Drift Baselayer Top and Bottoms
These are a great option if you simply want something to keep your children warm. Made of cotton, polyester and spandex mix, they’re soft to the touch and breathable and come in a range of contrasting modern, unisex colours so look great worn alone rather than just hidden under other layers. Wide elasticated cuffs (with thumb holes) and flatlock seams add to the comfort.
Available in grey, mustard, teal and navy, and from sizes 2-3 years to 11-12 years.
Buy now £36.00, Muddy Puddles
Tog24 Scafell Kids Thermal Set
Fantastic value, this set of base layers from Tog24 is lightweight and thin – ideal for fitting under heavier layers – but also provides enough warmth on chilly days. A quick-drying 100% polyester fabric, it wicks away sweat and keeps clamminess at bay, and the flatlock seams and stretchy, gently ribbed material make them really comfortable and easy to wear.
Available in black, and from size 116cm to 170cm.
Buy now £17.50, Tog24
Wedze Kids’ Ski Base Layer Freshwarm Black Top and Bottoms
One of the more serious looking sets featured here, the Freshwarm base layers are properly warm, with a soft-brushed finish inside and specific breathable inserts – behind the knees and between the shoulder blades. Featuring a turtle neck, gathered wrist cuffs and a wide elastic waistband, they’re designed to not let any draughts in. They’re not the most breathable here, and they don’t have flatlock seams, but it’s hard to be warmer for the price.
Available in black or plum, and in sizes from four years to 14 years.
Buy now £17.98, Decathlon
Kidly Organic Ribbed Tee and Legging
A great option for younger kids, these GOTS-certified organic cotton long-sleeved tops and leggings from Kidly come in a range of coordinating stylish tones and work equally well as sleepwear or, thanks to their slim fit, layers on colder days. The leggings in particular are a great fit for chunky toddler legs (that ribbing helps them keep their shape well), and the wide cuffs hold things in place. Unlike most here they don’t have flatlock seams, but our young tester didn’t seem to care.
Available in this navy, as well as eucalyptus, light grey marl, charcoal, khaki, mocha, brick, grape, petrol, camel and pine, and from three to six months to four to five years.
Buy now £24.00, Kidly
Reima Kinsei Thermal Set
Made from a mix of merino wool and Tencel (a regenerated fabric made from wood pulp), this Reima set is great value – especially at the current sale price (RRP is £50). The top and bottoms offer just the right balance of warmth, breathability and lightweight stretch, and our tester was never too warm and never too cold. There’s a slight dip at the back of the top to help it stay tucked in, and flatlock seams and labels positioned out of the way add to the comfort.
Available in this grey, as well as bright salmon, raspberry pink, powder pink and navy, and in size 80cm to 160cm.
Buy now £40.00, AlexandAlexa
Helly Hansen Lifa Merino Set
A detailed option from Helly Hansen, this set combines merino wool on its outer (for insulation) with Helly’s own Lifa material on the inner, an engineered polyester that works to quickly wick away sweat. Our tester was certainly very happy in this set and didn’t get clammy or cold. We like the fleece-reinforced knees and elbows and the addition of flatlock seams where they’re needed. Wide cuffs and a dipped hem at the back of the top complete the snug style.
Buy now £60.00, Helly Hansen
The Verdict: Kids thermals
Polarn O.Pyret’s Nordic set comes out on top for us – it’s the perfect combination of form and function, and the overall feel is snug and cosy. Reima’s set is seriously well made too, but if you’re looking for something cheaper Muddy Puddles’ set is also worth considering.