A prop completes a costume. A wand for a wizard. A sword for a knight. A stethoscope for a doctor. A magnifying glass for a detective. A staff for a wizard or warrior. The prop needs to be safely designed because it is something your child is actually holding and carrying around. The weight matters because your child will be holding it all evening. The construction should be robust enough to survive being carried about and waved around during play. These are the props that add the final convincing detail without being so large or heavy that they become impractical.