It takes a particularly narrow view of popular entertainment and literature to suggest that:
A) Fantasy has traditionally been aimed primarily at children--it hasn't. Fantasy, science fiction, horror, mystery & suspense, fairy tales and other speculative genres (including super-hero stories) have always examined adult themes and issues; generally moreso in their beginnings than they do today. This isn't a "revisioning," it's a return to their roots. Examine a few old issues of "Dick Tracy," "Batman," "Captain America," "The X-men," not to mention those popular horror and science fiction comics of the Golden Age to see what I mean. "Juvenile fantasy," maybe--but no more so than those produced by Poe, Lovecraft, Jules Verne, Arthur Conan Doyle, and other "adult" writers. "Moral ambiguity, horror, and sexual themes" are at the root of all fantasy genres, not just the modern ones.
B) That children's entertainment is inevitably "dumb, cheesy, wholesome" fun. Read Grimm's Fairy Tales or any one of the classic children's books from the nineteenth century: Alice in Wonderland, Peter Pan, Hans Christian Anderson, Mother Goose. There's nothing "dumb" or "cheesy" about those stories, and very little that's "wholesome." The same goes for superheroes (see above) and television shows. "Lost in Space"? A family alone in outer space facing danger and mystery at every turn--that can give a child nightmares just as easily as the murderous villain Sylar on "Heroes."
It sounds like this complaint is really about making adult themes more explicit in our popular entertainment (admittedly with debatable results), or, more likely, with some kind of yearning for the sentimentalized "wholesomeness" of the 1950s. For many Americans today, that era of cultural squeamishness, denial, and repression of all that is ugly in the world has somehow become equated to "the way things used to/should be." They seem to forget that there was a long history of literature, film, and fantasy before "Lost in Space." But it seems to me that it's that longing for the unrealistic "wholesomeness" of our least reflective era that should be perceived as "childish" and "juvenile"--not the more mature vision of these modern writers and film-makers, which is arguably the more "traditional" mode storytelling.
And oh, by the way, I feel quite certain that children have always posed their action figures/dolls/stuffed animals in "kama sutra positions" when their parents weren't looking!