My girls attended several Daddy-Daughter dances, which seemed more age-appropriate. They always wore something along the lines of an Easter dress -- you know, fancier than a typical church dress, but something they already had. They wore ribbons in their hair instead of make-up on their faces. They'd go out to dinner with Daddy at Pizza Hut, have pictures made, then have a fun evening with Daddy and friends.
This prom thing is kind of icky in that's encouraging the kids to have "a date" at much too young an age, and the miniature prom dresses are "too much".