No one ever said adapting a book into a musical was easy, and there have been more than enough failures (of the artistic and commercial variety) to bear this out. But whatever changes are made in the material - and even the best of adaptations usually make more than a few - what's vital is that the underlying spirit of the work remains intact after the transition from page to stage.

But the question of what an adaptation's responsibility is to the original source material, and an audience seeing the show that might already be familiar with that source, is always a difficult one. That proves to be the central question at the new musical at the Lamb's Theatre, Children's Letters to God, which Stuart Hample adapted from his best-selling book.

That book consists of nothing more than actual kids' letters to God, most of which run only a handful of words, on a wide variety of subjects. (One example: "You don't have to worry about me. I always look both ways.") With no plot, no characters, and little point beyond reminding adults of the eternal good-natured and hopeful attitudes of children, the book was one that sold itself completely on charm, and it had no trouble delivering that in spades.

In the musical, however, those letters are never the primary focus. When the letters are recited by the show's five cast members, they're intended to punctuate and amuse, but bear no real brunt of story; their connection to the plot Hample has provided for his libretto is nominal at best. The situations in that plot have been sitcom fodder for decades - the death of a pet, parents divorcing, one friend moving away - and the characters are similarly well-worn, with the good-looking boy all the girls love, the geeky boy who's bad at sports, the eternally sparring brother and sister, and so on.

If most of the songs from David Evans (music) and Douglas J. Cohen (lyrics) are unlikely to become classics, they generally fit the musical like a glove, finding much of the wonderment, mischievousness, and optimism of the pre-teen set. Songs about ant stomping, daydreaming during school, and being chosen second-to-last (rather than last) for a sports event are among the score's most memorable numbers, though none are unpleasant. (The musical direction is by Larry Pressgrove.)

The fair amount of magic the show is able to generate comes from the mixture of the straightforward story and the simple score; at times, the combination is irresistible and, yes, grin-inducing. Hample, Evans, and Cohen generally succeed at maintaining the precise alchemy that prevents the show from degrading from cute into cloying. The show sometimes seems disturbingly generic, and can wear a bit thin with its reluctance to take dramatic chances, but it still works a surprising amount of the time.

The cast members, all of whom are very talented and 15 years old or younger, are a big part of the reason the show does work so well. While Gerard Canonico, who plays the athletic Brett, stands out because his of charisma, professionalism, and polish, everyone gets a number of moments to shine. Libbie Jacobson is lovably melodramatic as the young Iris, Sara Kapner brings a nice uncertainty to her role as the older Joanna, Jimmy Dieffenbach is endearing as the awkward Theo, and Andrew Zutty is hilariously precocious as Joanna's younger brother, Kicker.

The direction by Stafford Arima and the musical staging by Patricia Wilcox keep them all looking good throughout, and employ the limited stage space of the smaller Lamb's Theatre to fine effect. That space is also filled by Anna Louizos's attractive backyard fort-inspired set, with the lights (by Kirk Bookman), sound (by Peter Hylenski), and costumes (by Gail Brassard) all complementing the experience nicely.

If that experience at times seems of the "let's put on a show" variety, and if one can't help but wish the show dug a bit deeper into its subject matter and approached the dramatic and entertainment complexity of something like last year's A Year With Frog and Toad, this one still works well. Family musicals truly appropriate for the whole family are difficult to find, but Children's Letters to God can be considered a mostly successful - if fairly minor - contribution to that genre.

Children's Letters to God
Running Time: 90 minutes with one 10-minute intermission
Lamb's Little Theatre, 130 West 44th Street between 6th Avenue and Broadway
Tickets online and current Performance Schedule: Telecharge