And you thought it was just kid's stuff: Children's books have traditionally been aimed at adults, but they are now becoming more grown-up, says John Windsor

Anne Renier was 73, in poor health and living in a quiet, tree-lined road in Barnes, London, when she sent out her husband, Fernand, to buy a copy of The Playbook for Kids About Sex.

A scholarly woman, she would have twigged that 'playbook' was not just an unfortunate turn of phrase. But we shall never know whether she was amused by this sex manual for pre-pubescents, with its full-page sketch of a blank frame and chirpy invitation: 'That's it. Draw a picture of your clitoris and other sex parts here', nor whether she was shocked by the book's suggestion that Teddy should participate in masturbation.

What we do know is that she catalogued the book, published in 1982 by Sheba Feminist Publishers, and put it with the 40,000 other children's books stacked floor to ceiling in the four- bedroomed house. Book cases and cardboard boxes were piled three deep, books lined the stairs and cliffs of books along the hall confined walking space to a foot-width, making passage to the kitchen a balancing act.

Following the death of the Reniers within four months of each other in 1988 the collection was checked and found to total about 80,000 volumes, which made it Britain's biggest and most comprehensive collection of children's books. It has since found a permanent home at the Bethnal Green Museum of Childhood.

The first exhibition drawing on the entire collection opens there next Tuesday. Its self-conscious title, 'Trash or Treasure', reflects the academic snootiness encountered in the past by the collection's full-time curator, Tessa Chester. In 1981, researching her librarianship dissertation on the sources of the Sleeping Beauty story, she was treated with condescension by librarians of national archives. 'I found myself continually having to justify my reasons for requesting material. The more ephemeral the item, the higher the eyebrows raised and the less help I received.'

A decade later, the pages of history textbooks are decorated with street literature and other ephemera almost as a matter of course. Few scholars now spurn the literature of everyday life.

That change is partly due to Anne and her Dutch husband, Fernand Renier. Like other great collections, theirs was inspired by a single insight. Not, like Robert Opie and his famous collection of packaging, that a Munchies wrapper, if discarded, might disappear from history without trace, but that material provided by adults for children can give a profound understanding of social history. Their in-sight is now accepted to the point of cliche.

The Reniers, who married after meeting at University College, London, at first collected the social and political history of the period 1780-1840. The virtues and vices, phobias and aspirations of the age, they discovered, were most accessible in children's books. Everything that grown-ups wanted to encourage or suppress in the young was there, especially in the work of also-ran authors.

The forthcoming exhibition has rejected chronology in favour of categories more accessible to children (such as animals, fantasy, penny dreadfuls - and sex, of course). But a quick glance at the displays reveals that, historically, accessibility to adults was equally important.

Children's literature evolved from 'chapbooks', cheap paper books sold by pedlars (or 'chapmen') between the 16th and 19th centuries. The chapbooks' characters such as Jacky Dandy were not aimed at children but at poorly educated adults, and wily publishers grasped that they could increase sales by putting an educational slant on their chapbooks, sometimes without even changing the woodcuts. Parents could then buy such trash with a clear conscience. So when Kendrew of York published The Cries of London in 1820 it added that these cries were 'for the instruction and amusement of good children' - which nimbly reverses accepted teaching that past ages treated children as defective adults. As late as the Sixties and Seventies, children were still having the pants bored off them by magazines such as Look and Learn, Finding Out and How and Why.

Sex, politics and religion, banned at the mess table, all found an outlet in books aimed at parents with children in mind. The Catholic Truth Society offered lurid titles such as The Young Lady Says 'No]' and So We Abolished the Chaperone. (Neither is what it seems: the second is not a sequel, and saying 'No]' meant rejecting marriage to a non-Catholic.)

To say that the history of children's books is the history of parents versus kids is not all that wide of the mark. Authors such as J M Barrie acknowledged the playfulness and fantasies of children, but it was not until modern times that publications such as The Playbook for Kids About Sex and The Little Red Schoolbook made an attempt to liberate children from grown-up tyranny.

The Schoolbook, translated from the Danish in 1971, resulted in the banning by W H Smith of Time Out, which published extracts from it, and its confiscation by police under the Obscene Publications Act.

It was deliberately subversive but imparted some shudderingly accurate home truths about grown-ups. Under the heading 'All grown-ups are paper tigers', it said: 'Children and grown-ups are not natural enemies. But grown-ups themselves have little real control over their lives. They often feel trapped by economic or political forces. Children suffer as a result of this. Co-operation is possible when grown-ups have realised this and have started to do something about it. If you discuss things among yourselves and actively try to get things changed, you can achieve a lot more than you think.' Seize it, lads.

What did Anne and Fernand think of all this? They never let on. Anne would say that she wanted the collection to speak for itself. Tessa Chester met them only once, shortly after becoming curator of the collection 10 years ago. Anne, almost invisible among the book stacks, was housebound, quiet, self-effacing. Fernand, who had worked for the BBC World Service for many years and had enjoyed a gregarious life, was still affable and an extrovert.

They had collected assiduously, visiting second-hand book shops, maintaining a network of alert booksellers and occasionally buying scarce volumes of their beloved Hans Christian Andersen through dealers at auction.

One of Anne's few publications, in The Book Collector, is densely academic. She appears to take more delight in finding a unique copy of Hannah More's rather dull The Middle Way's the Best from 1796, long thought to have been suppressed, than in the enchanted world of children.

Did the Reniers have a sense of humour? They undoubtedly did, Mrs Chester reports. Would Anne have been tickled by The Playbook for Kids About Sex? Tessa Chester thinks she would.

Not that the contents of such books can be openly displayed, even today. In the exhibition, you can see only the covers of the books and magazines, which are closed and taped up. Except for the notorious Oz School Kids Issue of 1971, the cover of which was thought too arousing. But even the rude words on the inside page 'displayed' are judiciously hidden by another exhibit. You can't be too careful with kids.

'Trash or Treasure': Bethnal Green Museum of Childhood from next Tuesday. Monday-Thursday and Saturday 10am-5.50pm. Sunday 2.30pm-5.50pm. Closed Fridays. Entry free.

(Photograph omitted)