I started with invitations which said "ALL NEW SUPERHEROES, REPORT TO SUPERHERO TRAINING." Inside, the invitations had the date, time, and location (Hall of Justice Training Center) and clipart of superheroes. All RSVPs had to come back with 5 pieces of information: true identity, special superpower, favorite color, favorite food, and favorite superhero. All this information was to be used later on. No costumes were necessary. Instead, we said in the invitation that capes and masks will be provided.  Both the parents and kids seemed to enjoy coming up with this personal information. Some kids responded by themselves which was great.