I question if the 7-year old is really old enough for serious winter camping. I agree with OM- camp out in the backyard. Graduate to car camping in the winter. Choose some weekends with forecast terrible weather so you can see what it is like. You can just get in the car and turn on the heater if things get epic. Be sure to really simulate a backpack trip- OK to have emergency clothing in the car, but really spend the day and night AS IF the car were not there. When all that is done, do some day hiking over snow or with snowshoes (or x-country ski) in order to get these skills honed. THEN, go on a winter backpack. I also agree that there should be one adult for each child until the child gets into the teens.