Some of the most common questions I get from the kids are the "Is that a real gun, or can I hold your gun?" I usually answer, yes this is a real Imperial issued blaster, and on the other I say either "It is against Imperial regulations to hand off or allow others to handle my weapon", or "No, children should not play with guns".
One of the best lines I have used at least once at every troop is when I'm taking pictures with someone and I say after the photo "Oops (or Wait), I forgot to smile." Always gets a laugh.