‘Sonny’ tests the tween climate

Here is Demi Lovato, just 16 and already a 10-year show-business vet: She got her start on “Barney” and last year was the female lead in “Camp Rock” (the Jonas Brothers movie) and she is enmeshed head to toe in the whole Disney star-making machinery, with a hit album released last fall on the Disney-owned Hollywood records and a new situation comedy premiering Sunday on the Disney Channel.

“Sonny With a Chance,” as in “of rain,” I guess -- formerly called “Welcome to Mollywood,” when the lead character had a different name -- casts Lovato as the newest member of a show within the show, a sketch comedy called “So Random!” Executive producer Brian Robbins co-created the actual Nickelodeon tween sketch comedy “All That,” and “So Random!” has a kind of authenticity that the sitcom containing it neither achieves nor attempts. (Creator Steve Marmel has written a lot for cartoons.)

There are two sorts of tween sitcoms -- the ones that star girls and the ones that star boys. The boys tend to be paired (Drake and Josh, Zack and Cody) in Two Stooges fashion, while the girls (Hannah, Carly, Sonny) are talented self-starters who dream big: Here, Sonny, a preternaturally nice girl from Wisconsin who posted funny things on the Internet, has been brought to Hollywood to join the cast of “So Random!,” which is, you know, like, her total lifelong dream. She is surrounded there by a complement of familiar types: a stuck-up blond girl (Tiffany Thornton), who isn’t a cheerleader but plays one on TV; a funny fat boy (Doug Brochu); a would-be Lothario (Brandon Mychal Smith); a strange little person (Allisyn Ashley Arm); and a good-looking fellow (Sterling Knight), who when we meet him is all full of himself but, as the only visible love interest for Lovato, will in the course of time be revealed to be not so bad after all. Former teen star Nancy McKeon, who is excited to live in a place where she can buy produce from a man standing at a freeway offramp, plays Sonny’s mom, but I doubt you will be seeing much of her.

There are some clever references to the adolescent entertainment world in which its stars all swim (they compete for “the prestigious Tween Choice Award,” etc.), but for the most part “Sonny” is subtle neither in form nor content. Like most kids’ shows nowadays, it is somewhat violently designed -- its main sets, which are riots of color, are like tween dream rooms writ large -- and performed. (I don’t mean to knock the talented cast when I say it’s pitched like a high school play.) There are jokes about butts and boogers and barf, as here, where Brochu’s character is upset that he has been forced to play an egg to Smith’s chicken.

“It’s not fair,” Bochu complains. “I always have to play the thing that comes out of you. . . . You played the mother, I played the baby. You played the stomach, I played the barf.”

Lovato, who has a low voice like Miley Cyrus’ and a comically mobile face, is very good, to the extent that it even matters. She is already a star, and her show was a hit from the very moment it was announced.

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robert.lloyd@latimes.com

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‘Sonny With a Chance’

Where: Disney

When: 8 p.m. Sunday

Rating: TV-G (suitable for all ages)