For my son's 6th birthday the theme was Batman.  I started by having the entire front porch lined with bats and a large photo of Alfred welcoming you to (our last name) Manor.  Once inside there were black streamers, balloons and old and new photos of all characters from the years of Batman history.  The full buffet lunch had named food like green Poison Ivy punch, Penguin pizza, Bane's bbq to name a few.  Throughout the house there were Batman accessories like batarangs for the kids to play with and made out of foam for them to throw once outside.  My son put Batman stickers on the sliding glass doors that led to the outside "Gotham City." I put our tent in the yard and covered it in an old white gauze canopy and covered it with large bats from Halloween for the Bat Cave.  The kids couldn't stay out of there with all the balloons that they had dragged inside to pop. I had gotten a large Batman poster to play pin the bat on Batman where the prizes were Batman hover discs.  The goody bags were blue bags with Batman lollipops, gummi snacks, and small various Batman toys. There were two cakes since there were about 55 parents and children at the house.  One had bat rings on the side and top that the kids got to keep once washed off and the other looked like Batman dropping into Gotham City on a tether line toward the Batmobile.  My son wore his Batman costume the entire day and after all presents were opened we took pictures of him holding each present and then sent that with the thank you cards a few days later.