What is it about Katie Morag, the children's character created by author Mairi Hedderwick? The child from the fictitious western isle of Struay seems to be a girl for all seasons, including Christmas.

That's why the Byre Theatre has invited Mull Theatre Company to bring Lisa Grindall's acclaimed stage adaptation of the Katie Morag stories to St Andrews for a December residency.

Not for the Fife theatre the traditional fare of cross-dressed pantomime dames and lurid double-entendres. Grindall's musical - in which the adventurous Katie Morag encounters her American cousins - may be about as Christmassy as a summer's day in Spain, but it has a child pulling-power that many a Scottish panto would give its eye teeth for.

This production, which first appeared on Mull in 2005, and which has been revived and recast by directors Fletcher Mathers and Gordon Dougall, was nominated for Best Show for Children and Young People in last year's Theatre Management Association awards. On this showing, it isn't entirely clear why.

Without a doubt, the show succeeds in transferring much of the innocent charm of the Katie Morag stories to the stage. Robin Peoples's sets, for instance, replicate assiduously the watercolour simplicity of the books' illustrations. Sally Reid has a rosy-cheeked, irrepressible good humour which makes her perfect for the lead role. Whenever she proclaims Katie Morag's much-loved catchphrase, "gee whilickers!", it really is as if Hedderwick's character has come to life.

However, there is a cobbled together aspect to the piece that leaves it trailing behind the best children's shows. There's fun to be had in the contrast between the tractor-driving Grannie Island (Sheena Penson) and the perm-and-twinset glamour of Granma Mainland (Annette Staines). The appearances of Eriska the (almost) talking horse are guaranteed to entertain the younger children. However, they are never quite enough to give the necessary sense of pace and direction to Katie Morag and her cousins' quest to find pirate treasure on Struay.

In changing its cast, the production has lost the services of some fine actors, such as Kevin Lennon (currently playing the hero in Jack And The Beanstalk at Dundee Rep) and Beth Marshall (who can be seen in the role of Mrs Darling in the Glasgow Citizens's Peter Pan). However, that in itself does not account for the show's shortcomings.

In this season of goodwill, one might be willing to overlook the often clunky set changes that punctuate this presentation, but the casting of non-singers in a musical is less easy to forgive. Reid is the perfect Katie Morag right up to the point where she is required to sing. She gets full marks for effort, but one suspects Andrew Lloyd Webber won't be calling any time soon.

The less said about the singing of performer (and, as the show's programme advertises, St Andrews café proprietor) Lawrie McNicol the better. His Scots-American father, Mr McShrub, has all the thigh-slapping cartoonishness required for Forbes Masson's fondly remembered pastiche pantomimes, but, like a careless shop assistant, he loses his notes.

Pamela Byrne and Allan Gilmour are in better voice as the initially repulsive (but soon converted) American kids Princess and Dude (no national stereotypes there!). Byrne's number, in which she sings about her triumph in the beauty pageant that made her Miss Florida Minicutie, is clearly intended to be as sickly sweet as Barbara Cartland's wardrobe, and comes close to postmodern genius.

Ultimately, however, for all its charm and bursts of energy, this somewhat rough-and-ready production doesn't live up to its considerable reputation.

Runs until December 29. Touring throughout Scotland in the New Year. www.mulltheatre.com