Swallows and Amazons, Old Vic, Bristol

"Better drowned than duffers if not duffers won't drown". Nowadays, Mr Walker would probably get arrested for the famous telegram permitting his four elder children to camp alone on an island on the basis that if they weren't self-sufficient enough to manage, they might as well be under the lake. Arthur Ransome's 1930 children's classic is altogether an odd choice for a dramatic adaptation, but the obsessive minutiae on boats and camping has mostly been scoured away, leaving a paean to children's imaginative capabilities and the burbling joy of putting to sea – well, lake – to prove that underage Britons never never never shall be duffers.

The set is ingenious in its lack of sophistication. The director Tom Morris understands that theatre is simply the best toy a child could want, and that anyone who lacks the wherewithal to mentally repurpose a couple of strands of wood as a boat, blue ribbons as water and flapping black plastic bags as dangerous birds really is a duffer.

John, Susan, Titty and Roger, crew of the Swallow, do have the benefit of stagehands, of course; they also have an onstage band, a proper enemy in the form of grumpy grown-up Captain Flint, and two seaworthy pirate girls, the Amazons, to war with.

It's odd that Helen Edmundson, who adapted the book with musical help from Neil Hannon of The Divine Comedy, has introduced so much dissent among the ranks: perhaps she can't conceive of a family who never argue, and certainly that is one of Ransome's most prodigious feats of imagination. There are other tweaks: the adults are no longer natives but slightly more politically correct barbarians, the story has been deftly adjusted for length and clarity and there's an odd prelude with an aged Titty, presumably to underline to children that this is Olden Times.

Mother, surely the gamest parent ever invented, is relegated to the background but the story has not, thankfully, been tamed: there is mayhem, if not quite murder, and small pirates will appreciate being drafted in for the big battle. Hannon's music is superb, although the cast – particularly Rosalie Craig as Susan and Amazons Celia Adams and Amy Booth-Steel – must do their considerable best with his banal lyrics. And I balked at a seven-year-old (Stewart Wright as Roger) sporting a beard, but then I am a barbarian. So drown me.

To 15 January (0117 987 7877)