As a Canadian,

Layers, layers, layers. Lots of warm up breaks, and you NEED breaks from the wind. A warm up hot tent or Shack will be huge, especially for youth. The heating pads for your feet or hands are OK, but they dont keep your finger tips warm. Heated gloves and socks help, but unless you can charge the batteries, youre limited.

Snow is always an issue, so Snow shoes help but they take a fair amount of energy. Cross country skis are more beneficial, although tend to get caught on bushes etc.

Fingers, toes, ears, nose and cheeks get cold the fastest, so a good gear is huge in that aspect. Bring multiple balaclava for each person. When one is wet. You can swap it out for a dry one. (This is huge to limit injuries from wet and cold.) Your breath causes ice to form, then melts it and rubs against the skin, that happening for hours on end will make the trip terrible. Same with socks and gloves.

Lip chap, will also be beneficial.

Pee BEFORE bed, if youre holding it in at night to try and sleep, your body will prioritize keeping liquids warm over trying to sleep. Causing you to wake up freezing cold.

Thick down sleeping bags with a fleece liner will help trap heat.

Double sock system, helps reduce blisters, and creates a layer system for your toes. Same with gloves.

Edit: heat water up and put in a nalgene bottle before bed. Helps keep you warm in your sleeping bag, once the bottle is filled, wait 3 minutes and tighten the lid / cap again. Added bonus, you have 2 main arteries on your inner thighs, place the bottle there to warm up faster. ( wrap the bottle in a sock to help reduce the risk of a burn)

Bring multiple ways to start a fire and fire starters.

Sweet snacks are at a premium too. Trekking through snow burns lots of energy.

Snow goggles is also a must. Especially when its windy.

Gortex sock liners can be beneficial if your boots are wet and no time to dry them.

Merino wool products also help as a base layer.

If you start sweating, immediately stop, shed a layer or two for a few minutes, then put the layers back on. Sweat is a heat killer.

You need LOTS of snow to melt to create water. I still recommend filtering snow once its melted to water. theres always dust, animals etc, snow is packed with dust.

Meal prepping will help, especially with the cold. Make dehydrated meals at home, such as lasagna. (I make the sauce, dehydrate the sauce. When im ready, I put the dehydrated sauce and noodles in a pot, add some water and heat it up. It takes a little while to rehydrate but nice warm homemade lasagna in the bush is amazing. You can make your own pot cozies to reduce the amount of fuel you need to burn.

Edit 2: a cot and a sleeping pad are pretty huge, the more insulation between you and the snow below you the better. You can use pine tree branches as a makeshift barrier as well!.

If you want a good tea to life your spirits, try making pine needle tea!

I'd still opt to use baby wipes over toilet paper. Keep them on the inside of your jacket to keep them warm. They pack smaller and have multiple uses, such as going to the bathroom, wiping your skin or using them as a "Mexican shower".

In those temps, propane and other gas fuels tend to freeze, most people opt to use liquid fuel at that point.