If you are heading to visit Santa in Lapland with an organised Lapland tour operator, find out first exactly what clothes they will supply and for what age of child the clothing suits - a number of companies do not supply clothing for children under 4 years.
Whatever clothes they do provide are very likely to be good and will give the warmth that is required in the garment. Most companies ask you to kit out your children with thermals, hats, gloves, socks, and balaclavas; some companies do not provide the footwear. The important thing is to check in advance so there are no unpleasant surprises en route to Father Christmas!
Layering is the key to keeping warm. Merino wool base layer is, in my mind, the best. Follow that with a cosy fleece mid layer and then a really warm snowsuit - a snowsuit is warmer than separates. There are lots of snowsuits on the market, so look out for the Scandinavian brands as they are designed for children who live and play in the Nordic chill factor.
Take a look at Raindrops kids' snowsuits, thermal base and mid layers.
Keeping the extremities warm can be the hardest:
Hands - choose mittens everytime as they are warmer than gloves. Get a nice pair of mitts that you can use as a base layer, and where possible a wool based mitt or glove. Then you need a really good pair of skiwear-style mittens that are not too tight but cover the wrist. Take a few pairs of heat pads so you can pop them inside the gloves if needed.
Raindrops children's mittens and gloves
Feet - the same applies with the feet. Choose a really good wool based sock that has a nice thick heel. Wool insoles are good for extra warmth and then really warm, good quality snowboots. Maybe take a set of footwarmers just in case.
Raindrops children's socks and snowboots
Hats - it is essential to keep children's (and parents') head warm so find a hat that protects the ears and neck too. It can be windy and there is nothing worse than ice on your face, so I recommend a balaclava (for adults too!) as a base layer and then a nice cosy warm hat with a fleece or furry lining that covers the ears. Trapper style hats are a good option. Fleece chubs - handy extras as you can use them to keep necks warm, or they can double up as a hand muff or to cover your mouth and cheeks if really windy.
Raindrops hats, balaclavas and chubs
Of course, as soon as you and your children meet Father Christmas, you will forget about the cold and your hearts will be filled with warmth and Christmas cheer. Lapland is the most magical place at Christmas time - so stay warm and enjoy the experience!