BOOK REVIEW / Imaginary journeys of a daydreamer: 'The Daydreamer' - Ian McEwan: Cape, 8.99

THE GREAT dreamers of literature - from Don Quixote to Walter Mitty - win us over not with charm or brainpower but by the sheer force of their foolishness. In a world dominated by cynical and knowing realists they offer guilelessness as a virtue and remind us that innocence is superior to experience, that only bores see windmills where they could, if they wished, see giants.

Peter Fortune, the boy-hero of Ian McEwan's exhilarating first book for children, slips into this tradition with ease. There isn't much in the teen-fiction bracket that includes quotations from Ovid, snowy fantasies borrowed from Jack London, characters called Tamerlane and pastiche Kafka. But McEwan manages to combine high literary reflexes with a raw domestic simplicity that is thoroughly affecting. People will say that he works on two levels - the childish and the adult - but in truth it is hard to discern the gap. The Daydreamer is a book about unrequitable longings, and children do not have a monopoly on those.

Peter Fortune is a quiet boy with a busy head. His teachers think he's dull, staring off into space all day, but he has nothing worse than an excessive imagination. His world seems limitless - think of infinity and double it. In his dreams he fends off wolves, wrestles with dolls and exposes burglars with the aid of that perfect wonderland haven - a real mousehole. He can magically become a cat, or a baby; he even spends a few traumatic moments as a grown-up. Trying on all these lives for size is both flighty and educational: when he infiltrates the black fur of the family cat - after a brilliant unzipping scene in which the pair swap bodies - he enjoys a day of gorgeous feline laziness and fierce nocturnal vitality. As a baby he drowns in banana and plastic toys and comes to see the narrowness of the huge little boy (himself) who is being so unfriendly.

These imaginary journeys leave Peter bruised but wiser: making his family disappear helps him to register his love for them. This might make the book sound like a cute morality tale, but it throbs with an appealing and anarchic if-only fervour. The governing idea - a heady secret world closed to adults - ought to be enough to make a young heart leap. And the children in the book have the right sort of swaggering superiority to know- nothing adults. At one point the 10-year-old Peter goes into the room he slept in last year and broods: 'He'd been just a kid then. Nine] What could he have known? If only his 10-year-old self could go back and tell that innocent fool what was what. When you got to 10 you began to see the whole picture, how things connected, how things worked . . .'

Later, Peter gets to rub Vanishing Cream on his parents and his sister to make them disappear. It is clean, unthreatening fun - 'She was the only mother he knew who could stand on her head unsupported, but he had made his decision, and she had to go.' But McEwan cannot resist exploiting the more chilling possibilities as well. Peter's sister is too quick to fall for the vanishing trick (children are harder to fool than parents), so gets only a dab on her head. Sawn off at the neck, she runs around the garden trying to escape: 'She would have been screaming if she had had a mouth to scream with.'

There have been murmurs to the effect that McEwan's taste for the ghoulish is not quite the thing for a children's book. But the odd tremors of violence - when the dolls rip off Peter's arm and leg, for instance - seem wholly innocent, merely surreal. Kids used to Deathstar Five Thousand and Planet Zog Multikiller video packs won't raise an eyebrow. The more shadowy aspect of the book is its undertow of grief about growing up. For all its levity and gracefulness, this is a never- never land with clouds on the horizon - and it echoes with the knowledge that the magic is fleeting, that it will fade and die.

Or that it will change, at any rate. The overarching theme is metamorphosis. In McEwan's Whitbread-winning novel, The Child in Time, one of the characters - a children's book publisher - wrote out the recipe for The Daydreamer when he expounded on the function of literature for kids. The distinction between adult and children's fiction was a fiction of its own, he explained. The best books gave readers an intimation of mortality, a hint that childhood was not infinite. The Daydreamer is just such a book: its playfulness includes sober gestures towards the disappointments that lie ahead. In the brilliant final chapter, on holiday in Cornwall, Peter runs around on the beach with the gang, laughing at the tedious parents who do nothing all day except wonder what to have for dinner. But then he has what we would call an epiphany (to him it's a nightmare):

'Standing there that August evening between the two groups, the sea lapping round his bare feet, Peter suddenly grasped something very obvious and terrible: one day he would leave the group that ran wild up and down the beach, and he would join the group that sat and talked. It was hard to believe, but he knew it was true. He would care about different things, about work, money and tax, cheque books, keys and coffee, and talking and sitting, endless sitting.'

McEwan is not, thank goodness, out to draw hippie contrasts between glorious dreams and the banality of everyday life. The dreams in this book are a central part of life: that's the whole point. They are both provoked by it and act on it. When Peter confronts the school bully, Tamerlane, in a playground square-up he realises that he has only dreamt the yob's fearsomeness. All that he and the other children have to do to end his reign of terror is wake up. It turns out that Tamerlane is the same as the rest of them: a boy with a teddy bear who sometimes has to do the washing up.

The book ends well, with an uneasy waking-up scene that both embraces and celebrates an authentic adult impulse. In a parody of Kafka's Metamorphosis, Peter wakes after a night of troubled dreams to find himself transformed into a 21-year-old. This happens during the holiday in Cornwall where the children - the Beach Gang - have been having adventures while their parents plan the barbecue. The Kafka echoes reinforce the sense of alienation: it is as if all adult life were a treacherous setback. And, at first, Peter is bemused. But then, in a lovely turnaround, he finds himself trembling in a railway tunnel with a 19-year-old girl called Gwendoline ('Morning sunlight, broken by the leaves of the apple trees, bobbed about her shoulders and in her hair'). Unimaginable pleasures rush upon him, and he hits on a big truth: that even adults have secret dreams. Suddenly the grown-up world, which all along has seemed a diminished version of the fantastic imaginary places, doesn't seem so bad after all.