Why should I feel nostalgic for a childhood I never had? The Lake District, in which Arthur Ransome set his book Swallows and Amazons, is a world away from the north London suburbs of my youth.

In Swallows, the four Walker children have an infinite landscape of rolling hills and mysterious lakes in which to play. They have parents who let them roam wild and camp out over night. And they are polite, well-spoken and well-educated enough to make casual comparisons between their adventure and the Spanish conquistadors.

Yet by the end of this Bristol Old Vic stage adaptation of Ransome's 1929 classic children's story - which arrives in the West End with deserving support from the National Theatre - I found myself unexpectedly experiencing a deep affection for a pre-war, bucolic England I never knew.

And the reason has everything to do with the thoroughly modern way in which Tom Morris's production resurrects Ransome's old-fashioned world. The stage is populated by a core cast of adults playing children, a device that touchingly reveals the child in all of us. But there are also multi-tasking stagehands who double as the musicians who play Neil Hannon's score.

Though described as a musical, Swallows feels more like a play - written by Helen Edmundson - though one with plenty of music in it. And when the music stops, it is taken over by the kind of playful, inventive theatre techniques that ignite imaginations of all ages. When, for instance, the Walker children use a telescope as they sail across an "uncharted" lake, a stagehand springs into action with two cardboard circles bringing them together to form one ring. It is the perfect impression of a focusing lens.

And who knew that the sound of a campfire could be depicted so convincingly with just clapping hands and the clicking of fingers?

The result is a show that feels hand-made and gets to the essence of everything it attempts to depict - from the snap and crackle of a campfire's flames to the deep sense of injustice felt by children when adults behave unfairly towards them.

For injustice is the overwhelming emotion when John, the elder Walker boy and captain of the boat Swallow, is accused of crimes he did not commit.

Stewart Wright, physically the biggest adult in the cast, plays Roger, the youngest of the Walker children, with a hilarious and endearing earnestness. In fact, all the cast transmit the guilessness and body language of childhood.

As a result, the innocent spirit of adventure, which is what makes Ransome's book so appealing, is captured perfectly.

The children I took to the show - two nephews and a niece, whose ages range from six to 11, roughly that of the Walker children - were all utterly engrossed. And so was I.