What is an easy party game for 3-10 year olds?

I am admittedly very lazy so I'm looking for a game that requires little set-up and supervision. My son is turning 4. Our party is only for family but we have 18 kids in the family who will attend, ages 1 month to 13 years with the majority between 3 and 6 years old. I will be playing pin the tail on the donkey and musical chairs, but need one more game.