Blair Treu’s “Little Secrets” is one of those family films that’s so intent about offering positive messages that sitting through it is a chore instead of a pleasure. Sugary sweet, heavily didactic and relentlessly uplifting, it should probably come with a warning that diabetics could be endangered by watching it.

Jessica Barondes’ script centers on Emily (Evan Rachel Wood), a middle-class teen and aspiring classical violinist who’s about to audition for the local youth orchestra under the tutelage of her supportive tutor Pauline (Vivica A. Fox). At the moment she’s an only child, but her mother is now unexpectedly pregnant, and she feels some discomfort at her parents’ excitement over the imminent new arrival. Emily also has a curious little business on the side: she acts as sort of a clearing-house for the guilty secrets of the kids in her neighborhood. Whenever they break something or otherwise mess up, they confide their peccadilloes to her, and (for a nominal price) she hides away evidence of the wrongdoing in paper bags kept under lock and key. Naturally, Emily has a major secret of her own, and it will take a crisis (involving a whole pile of coincidences) for her to get the courage to reveal it.

All the changes in Emily’s life occur during the summer, when her closest friends are away at camp and she gets to know the family that moves in next door, especially Philip (Michael Angarano), a kid a few years her junior who takes an instant liking to her. Unfortunately, Philip has an older brother named David (David Gallagher), who’s absent most of the summer but catches Emily’s eye after he returns. Ultimately everybody learns that secrets are bad–big or little–and that honesty and friendship always pay.

Some of “Little Secrets” is likable enough–Wood, though her character is a trifle too prim, is a pleasant young actress, and Angarano sparks things with his winningly goofy charm, though he occasionally lays it on too thick. Technically, too, it has a crisp, colorful look, and it’s decently mounted. But overall the picture wears its heart all too obviously on its sleeve, especially since the central conceit–about Emily acting as a sort of neighborhood conscience by storing all the children’s secrets–seems contrived and clumsy from the moment it appears. Treu, meanwhile, moves things along much too slowly; the sluggish pace merely accentuates the feeling of heavy earnestness, and by the time we reach the final act, the picture is nearly dead in the water. A brisker approach would have been advisable.

Parents searching for a totally inoffensive movie may embrace “Little Secrets.” In reality, though, it would be more at home on some family-friendly cable channel than the big screen. Commercial interruptions might even help dilute the oppressive niceness of it all.