On December 18, 1954, a frustrated reviewer issued a call to arms: 'Adults of all ages!' he wrote. 'Unite against the infantilist invasion.' The book that provoked Maurice Richardson's rant? The Two Towers, the second part of JRR Tolkien's sprawling trilogy Lord of the Rings.

Adults of all ages were distinctly unpersuaded. Instead of uniting against childishness, they gobbled up Tolkien's works so greedily that the Lord of the Rings became the third best-selling book of all time, with an astonishing 150 million copies sold worldwide. Its smaller, lighter prequel, The HobbitMost of the characters in Tolkien's fantasy world (elves, dwarves, goblins, trolls) are stolen from Norse and Anglo-Saxon mythology. But hobbits, small home-loving creatures with hairy feet, are his own invention. In The Hobbit, or There and Back Again, the hobbit in question is Bilbo Baggins, who goes on an 'adventure' with a group of dwarves to reclaim the treasure captured by a dragon named Smaug., sits just one place below.

Peter Jackson's film adaptation of The Hobbit is released this week. And despite a mixed reception from the press, this first episode in the adventures of 'halfling' Bilbo Baggins is tipped to join the ranks of cinema history's highest grossing hits. It will fit in nicely: not only are three of the top thirty slots taken up by Jackson's Lord of the Rings movies, but they are surrounded by other films that were either made for children, or based on children's stories.

This year alone, the top ten box office hits include three reworkings of children's books, three comic book adaptations and two original cartoons. The only two that are clearly aimed at adults are a James Bond film and a story whose main star is a giant teddy bear.

Some critics object that The Hobbit, which hints at horror and violence beneath the swashbuckling plot, is not really a children's film at all. 'Tolkien wrote a book for kids,' said Total Film, 'but Jackson hasn't made a movie for them.'

Yet that in itself is revealing. Just as recent Batman films have introduced notes of psychological menace and realism to a previously lighthearted franchise, Peter Jackson has emphasised the darkest, most adult undertones of what started out as a simple fairy tale.

What, ask the likes of Maurice Richardson, has happened to our culture? Have we lost the ability to cope with serious, adult art? Once upon a time, great novelists like Charles Dickens and George Eliot topped bestseller lists with books that unflinchingly explored the social realities of their time. Today, they say, these works have been replaced by silly, childish fantasies. Our culture has become pathetic.

What cloying snobbery, say Tolkien's fans. A film full of dwarves and wizards can carry just as much emotional depth as one populated by politicians or policemen - and convey messages just as profound. Children are willing to accept fantasies because their imaginations are supple and free, they say; if adults can follow their example, so much the better.