Invest in a nice pair of snow boots. A really nice pair. Ugg actually makes some very nice sturdy winter boots. Haven't been through a German winter yet, (I hang out here to learn German because I'm moving there next year) but I'm from a warm climate and I spent a winter in rural Oregon for a job a few years ago. They had over a foot (~0.3 meters) of snowfall that year. The first thing I bought was a pair of snow boots. The second was a much better pair of snow boots. Get a good winter jacket, gloves, and some ski pants, too. Walking on ice is also something pretty new. Tell them to keep their feet directly under them. That advice helped me out a lot.