For girls two and up:
-princess party (all girls come dressed as their favorite princess)
-tea party - again, little girls in dresses!
-"spa" day - depending on the ages: hair/nails/facials/makeup (get parent's permission!)
Boys two and up:
-Visit to a local fire or police station
-"ball" party....baseball, football, basketball - dress as your favorite team/player
-hunting party (although some girls would like this too) - everyone comes dressed in camo or orange!
....and of course, you can always do a party based on a movie or TV show and have guests come as their favorite character!