it all depends on their ages. I'd treat it as any other. If they are old enough... some finger foods (small sandwiches, chicken nuggets, veggies etc.) Drinks -- water, juice, maybe some apple cider or some other sparkly drink (add seltzer water to juice) for the big moment (can even get plastic "champagne" glasses to make it extra special.
Activites: whatever you have available. Depends on the weather. Here was did bounce house one year but its warm out. Some movies is always good. Last year we had 6 (ages 31/2 to 6) put an air mattress against the wall and just kept running against it - entertained them for hours. Maybe some music they can dance to. Some easy to share/pick up toys. It all depends on the ages and personalities.
at 11:10 AM on Dec. 30, 2010