There is a reason that kids love Elmo: He is a cute little lovable monster with a funny voice on their television who teaches them that the letter "Z" is hilarious. Now take that vision of Elmo and blow him up into a real-life 5'9" red monster of body odor who has a nasally voice with a hangover rattle and a "magic box" of candy, and who could possibly blame them for being scared? The question we should be asking is: Why are the kids the only ones at the party who seem to get this? There has never been a parent in the history of time who, instead of making their screaming child take a picture with the thing they currently fear most in the world, has said:
"You know what? My 3-year-old's instincts on this are something that I should probably be encouraging. Maybe I shouldn't force her into the arms of what she perceives to be either a fire monster of death or just a strange man in a mask. I'm going to let her just go hang out at the swings until she has matured enough to realize that it's a real novelty to have a grown man who has chosen the parachute game as a career trajectory just wandering among us."
"He won't eat you. He only eats 99 cent frozen burritos."
Now there are different levels of fear, depending on the costume; Pikachu scares the shit out of kids, as do all of the Teletubbies (especially together). Clowns tend to be a mixed bag; some kids are terrified of them, and some are too stupid to know any better. But G.I. Joe ... well, G.I. Joe is special. Never once did I go to a party as G.I. Joe in which all kids weren't thrilled by the end.