“I like old things,” says Emma Roberts in “Nancy Drew,” a new film based on the venerable book series about one teenager’s bloodless war on crime. Nancy’s affection for the old, and for the particular strain of do-good ethics that she has inherited from her widower attorney father, Carson (Tate Donovan), have made her an avid amateur detective. Within the first few minutes of Andrew Fleming’s modest, polished, and surprisingly ingratiating film, Nancy has stopped a robbery, hammered out a plea bargain for the thieves, resolved a hostage crisis, and foiled her own kidnapping by rappelling down the side of a church in penny loafers. Clearly, she is on the verge of losing her amateur sleuth status.

A lucrative consulting gig in Los Angeles requires Nancy’s father to temporarily relocate to the West Coast. Since the family that stays together stays together, Nancy must also bid adieu to the bucolic, time-warped town of River Heights, her blue Nash Metropolitan roadster, and her semi-beau Ned (Max Thieriot). In one of several savvy but subtle directorial touches that distinguishes Mr. Fleming’s film from the rest of the ‘tween movie pack, the director underscores the transition between Nancy’s anachronistic Midwest life and modern L.A. using hypnotic time-lapse photography and photographic dissolves.

Carson is determined that Nancy give up her sleuthing ways for the duration of the Drews’ L.A. sojourn. The criminals in the City of Angels play by tougher rules than do the comically bumbling retro-crooks that the tree-lined, not-very-mean-streets of River Heights breed. But before they’ve even arrived at their new home, a run-down mansion formerly owned by a vanished movie star, Nancy already is puzzling out the mystery that has made it possible for her dad and herself to rent in such dilapidated splendor.

Nancy is tossed into the social deep end as a transfer student at Hollywood High, where her classmates nearly sprain their necks sizing up and making sense of the old school “new girl.” For 100 painless minutes, “Nancy Drew” intertwines the mystery of the missing screen diva Dehlia Draycott (played in fake film clips and speculative flashbacks by Laura Harring of “Mulholland Drive”) with a standard-issue, post-“Mean Girls” fish-out-of-water movie scenario, complete with eye-rolling, slack-jawed Rodeo Drive mall rats, crashed parties, and capricious on-campus humiliations and hazing.

In and around the tepid car chases, G-rated violence, and endlessly budding, rigidly chaste romance, “Nancy Drew” has some things to say that are worth hearing. I don’t think I’ve ever seen a children’s movie that goes to the lengths this one does to remind its target audience that critical thinking and genuine curiosity about the world are as vital to health and happiness as church, family, love, and loyalty.

The child in us is always on the lookout for kid movie fare crafted well enough to negate an adult’s well-earned aversion to condescending, inept, or disingenuous storytelling. “Nancy Drew” is nowhere near the glorious Pixar extreme edge of that scale, but it’s closer than its ad campaign might lead parents with a fear of the Saturday morning multiplex to think. As a gentle rebuke of contemporary mores, it’s actually more effective than Pixar’s last film (and thus far only dud) “Cars,” a movie that, like “Nancy Drew,” maintained that personal growth is fostered by honoring old ways as much as craving new and novel experiences.

At the very least, the film offers a cheerfully sketched widescreen caricature of a Los Angeles whose crass and corrupt surface of spoiled kids, conniving attorneys, and spaced-out spinsters barely hides a bottomless show business gothic morass of “Hollywood Babylon”-style shattered lives and discarded dreams. In other words, the City of Angels in “Nancy Drew” is not all that far removed from the real thing.