Blindfold the neighborhood kids, tie their shoelaces together, dress them in dark clothing, and have them run repeatedly across an active roadway at night. If that doesn't seem too bright to you, reflect on the fact that the equivalent handicaps are pretty prevalent on Halloween night anyway. Refuse them, even if you have to put up with a tantrum. The old-school elastic masks are better, but as anyone who remembers their favorite Collegeville Costume will know, there is no such thing as peripheral vision in a Halloween mask. There's a better solution.
Some costumes now come with masks that sit on top of the head, that the child nods down to expose.
A lot of them look very good. Better costume shops offer a variety of lower-face masks, that cover the nose, or nose and mouth. And absolutely nothing beats some imagination, odds and ends, and make-up. You may even have some fun together in the process. Give it a shot.