wow, i started this thread a year ago and it's still going! i've been looking at costumes online just for some ideas, and again am bombarded by "sexy" versions of everything.
an old article, but of some interest to this ongoing conversation about very young girls dressing slutty:http://www.newsweek.com/id/62474
"The hypersexualization of younger and younger girls only serves to reinforce gender roles. When an 8-year-old girl can't find a doctor costume because all they have are nurse outfits, that's a problem."
and from one woman's book, which includes a chapter on halloween costumes:
Of the 22 girl costumes featured on one Web site Lamb looked at, 15 were cheerleaders, divas and rock stars. "That really limits girls' imaginations," says Lamb, who surveyed 600 young girls for the book, many of whom admitted to dressing up as something sexy for Halloween in order to get attention.