Children’s Christmas entertainment is as traditional as mince pies. Even in its bastardised manifestation, the modern pantomime, an opportunity for “adult” jokes about royals and television made by sports and soap celebs, some things can be relied upon: Dick Wittington will get to London, Cinderella will marry the prince and hundreds of sweet-stuffed children will screech “Behind you” in unison when incited to do so by a man in a blond wig and vast spotted drawers.

But oddly enough, the underlying theme is change, transformation, growing up, for this was what the original tales were all about when they were as yet unmixed with music hall. Silly Jack finds courage to make adult decisions up that beanstalk and Sleeping Beauty and Snow White experience sexual awakening.

The two most eagerly awaited children’s shows in London this season, Peter Pan and More Grimm Tales, come freighted with tradition, yet both are fresh and address the pleasures and agonies of change, especially from childhood to independence. Peter Pan, with its flying but bosomy “boy” was a regular feature of middle-class Christmasses for more than half a century after its first performance in 1904, and famously appears to deny the necessity for change: Peter Pan is the boy who never grows up.

In the National Theatre’s version, by Trevor Nunn and John Caird, which attempts to be true to JM Barrie’s original intentions, and reflects the tragedy in the playwright’s own life, a more complicated, melancholy, magical play emerges - with a young male actor in the title role. This year’s script is a development of the one first performed in 1982 by the Royal Shakespeare Company at the Barbican.

At the Young Vic in 19934 Tim Supple directed Grimm Tales, a presentation of 10 of the stories, in a new, spare but clear and speakable retelling by the poet Carol Ann Duffy. That production, minimally staged, relied on the physical and storytelling talents of the cast and became a touchstone for children’s theatre in the 90s. Primary school spectators familiar with television and computer wizardry were so transported into another world that, when the actors threw imaginary food in “The Magic Table”, the audience caught it and chucked it right back. That incident came about almost by accident when an actor “threw” one evening on impulse, but its adoption indicates Supple’s openness (and that of his chosen actors, for the first time, thanks to Arts for Everyone money, an established Young Vic Company) to audience reaction. Quite a different thing from manipulated “participation” in the “Behind you” sense.

More Grimm Tales features the same artistic team, including Adrian Lee, the composer and director of music, now joined by associate director Barbara Houseman. There is no shortage of material: the Grimm brothers - German philologists and students of folklore - having collected 201 oral tales. Each, say Supple and Houseman, still resonates, despite translation, with the distinctive voice of the speaker whose words the Grimms wrote down. “You should still hear that, through the filtering of the actors, even if it is shattered into a dozen voices,” says Supple.

This time there are 16 tales. Some will take only a few minutes to make a point, like “The Ungrateful Son”, about a man whose roast chicken, meanly unshared with his father, turns into a toad and adheres to his face. The old favourites - “Snow White” and “Little Red Cap” (more often called “Little Red Riding Hood”) - are probably the most familiar, with “The Musicians of Bremen” and “Rumpelstilts-kin” not far behind. The evening ends with “Brother Scamp”, described by Supple as “an Everyman parable in which an ex-soldier is visited by St Peter, who tests his goodness and generosity”. Brother Scamp lives by his wits, getting what he can from other people, but without unkindness until, in a satisfying twist at the end, he tricks St Peter into letting him into Heaven.

Transformations and journeys recur in the tales, as does death - that of the wolf in “Little Red Cap”, who is slit open with a knife, of Snow White, who is resurrected, and of her stepmother, who dances to death on hot iron shoes, and of Rumpelstiltskin, who is torn in two. Violence is inherent in these tales, yet there is a distancing which makes that palatable. As Supple explains: “They are in code so that everyone - grandmother, father, teen-ager, child - could listen together. The tales have great wit, deep wisdom and far more sophistication than if they were targeting one group. “Snow White”, for instance, is a metaphor about the terrifying and painful process of finding independence. Until she loses her mother-figure, she can’t grow up.” The queen is facing the necessary process of ageing, of handing over to the next generation. She represents an element common in human experience rather than a character with whom we should identify.

Supple thinks any explicit morals were almost certainly tacked on by the Grimms. “The wolf shows Red Cap flowers and beauty; there would be something missing in her life without the wolf. If we interpret the stories morally, we limit their power.”

Carol Ann Duffy has worked from a variety of translations, giving the tales, as Supple puts it, a “living voice for the modern ear”. He agrees with Houseman that the language is “the tip of an iceberg: below that is the imagery and deeper still a specific psychological world that is concrete, mystical, witty and comic”.

If Grimms’ Tales have survived from a pre-literate time, JM Barrie’s Peter Pan must be the most written and re-written play ever. John Caird indicates his “bible” - a complete set of all Barrie’s versions, alterations and deletions. It is a good three inches thick. The 1982 NunnCaird Pan was the 1928 version with whichever of the variations they chose to import, including some from the 1911 novel. They included a poignant final scene, which had only ever been previously performed once, in 1908, in which Peter returns to visit a grown-up Wendy, now a mother herself. The gap between the perpetual boy and the other children, now responsible office-going adults, is painfully clear. Caird and Nunn also invented a storyteller - Barrie himself - in order to include some of his richly “whimsical, ambiguous and ironical” stage directions. Further changes have been made in 1997, including the addition of more music by Jonathan Dove to the late Stephen Oliver’s haunting score.

Caird points out Barrie’s most revealing comment about Peter, a programme note for the 1908 Paris production: “Perhaps he was a little boy who died young, and this is how the author conceived his subsequent adventures. Perhaps he was a boy who was never born at all - a boy whom some people longed for, but who never came.” For Barrie’s own history is inextricably bound up in Peter Pan’s. His beloved older brother, David, was killed when Barrie was 11. He attempted, unsuccessfully, to replace him in his mother’s affections, even aping his voice, and he never really recovered - he scarcely grew physically after the tragedy. As an adult he remained childless but sought solace in the company of children, in particular the five Llewellyn-Davies boys with whom he played piratical games in Kensington Gardens and to whom he dedicated the play. It was, he wrote, “streaky” with them. By 1910 the boys were orphaned and Barrie became their guardian. Their mother, Sylvia, represented the ideal of motherhood, personified by Mrs Darling.

Tragedy dogged the Llewellyn-Davies family, a story chronicled by Andrew Birkin’s book Peter Pan and the Lost Boys. Michael, Barrie’s favourite, died in a swimming accident when he was an Oxford undergraduate and both their parents died young of cancer.

Caird says that Barrie “knew everything there was to know about childhood. He is ambivalent about growing up - it’s a tragedy if you do and a tragedy if you don’t. He was still close to his own childhood; most people forget what they felt before the upheavals of adolescence. Every child knows what it is to be in love, to feel deeply enough to cry themselves to sleep. This love story, between Peter and Wendy, is doomed - and that is close to children’s knowledge of the world.”

Caird helped his cast to remember their childhood by bringing in 30 eight to 12-year-olds for a day and getting them to invent plays with groups of actors. This led to hilarious moments - “Ian McKellen (Captain Hook) as a toothless crone in a bonnet and Alec McCowan (the Storyteller) wearing a mob cap in a laundry basket.”

Peter is “heartless”, almost gleeful, a lord of misrule - Barrie complained that the statue in Kensington Gardens failed to capture the devil in him - but this is a typical quality in children, says Caird. “They don’t understand other people’s pain or see through others’ eyes - nor should we expect them to. ”

Barrie is himself present, believes Caird, “significantly in the character of Peter. He is in Hook too - the dark humour, his pleasure in frightening children - but JM Barrie was really Wendy. His relationship with the boys was maternal; he shared Wendy’s practicality and protectiveness, and Wendy was able to express adulation for Peter, which Barrie was not able to do openly to the boys. This was a stroke of genius; there had been no girls in their real games.”

Caird’s enjoyment of the discussion is palpable, but he warns: “Life, thought, artistic inspiration - these are complex and to ‘explain’ too much can become banal. Barrie, however, knew very well what the well-springs of the work were.”

And just in case anyone should think solemnity has won the day, Daniel Evans is having a high old time as Peter, practising flying through the set of Guys and Dolls which still occupies the Olivier stage.

More Grimm Tales at the Young Vic: 0171 928 6363; Peter Pan at the National Theatre (Olivier): 0171 928 2252