Those panties become long johns at those temperatures. As is depicted.

We do usually put a thin balaclava for kids already at much lower temps. It covers the neck and also prevents snow from going down clothes a little.

also wearing nothing but a tank top and shorts at 20°c, it takes at least 25° for me to reach that point.

you don't need as many layers but really your clothing should account for situations where you may be stranded

-14c in a hoodie is fine up until you're 10-16 minutes outside and your body heat is gone (numbers not exactly accurate but hopefully you get an idea of what I mean)