+1 Allen & Mike's Really Cool Backcountry Ski Book
+1 the kids will get wet and cold

besides hot chocoate and handwarmers, bring nalgene bottles that you could pour boiling water in, put a sock over, and have a hot water bottle to warm them up.

My daughter and her friends *LOVED* winter backpacking, or in our case snowshoeing. The kids loved building snow structures for camp like... othouse, kitchen, platform for shelter and/or snow cave. We haven't made an igloo, would love to try sometime.

--Mark