make and choose the best snowman for prizes, I like the idea above with the cake and hot cocoa. If can maybe a skating party. treasure hunt and find winter items like gloves, scarfes, balls, etc. You could even do up some sormores.
i would do some scavenger hunt,snow man challenge,little stuff like that...divide up the kids and adults with the kids and have a snowball fight and go sledding..then go have cake,hot cocoa inside and let the kids warm up and play...i think the kids would have a blast