Gay, Hispanic, Adoptive: A Triple-Threat Family "The Fosters" is a conventional family dramedy about an insistently unconventional family: lesbian mothers (a white police officer and a black charter-school administrator), the officer's biological son, adopted Hispanic twins and a foster daughter fresh out of juvie. This demographic engineering is so obvious that in the show's premiere, to be presented on Monday on ABC Family, even the characters notice it. The newly arrived Callie (Maia Mitchell), sporting a split lip and a healthy cynicism from her time in prison, looks at the little rainbow coalition gathered around a suburban San Diego kitchen table and says: "So you're dykes. And he's the real son. To its credit, the show, created by Bradley Bredeweg and Peter Paige, treats this not as a teachable moment but as a comic beat. The police-officer mom, who hasn't met the new addition to the family, asks her partner, "And who's this?" Ba-dum-bum. Cut to commercial. ABC Family always has a place on its schedule for issue-oriented teenage melodramas like "The Secret Life of the American Teenager" (pregnancy), "Huge" (body image), "Switched at Birth" (disability) or "Lincoln Heights" (race). "The Fosters" (which makes its debut after the final episode of "Secret Life") is a multiple threat, wrapping up gay parenting, blended families, adoption and the foster care and juvenile justice systems in one happy-sad package. On the basis of the pilot, the show does a slightly better than average job of turning off-the-shelf ingredients into something diverting and occasionally moving. Beneath the 21st-century family structure, the elements of the story are familiar: loving, nervous parents; secretive but good-hearted teenagers; fitting in at school, demonstrating loyalty, learning which adults to trust. The conflicts and crises are handled with a mostly light touch and sometimes with what approaches sharp humor, usually in scenes involving Teri Polo as the divorced police officer, named (believe it or not) Stef Foster. Ms. Polo does tough-but-caring with panache and is gracefully funny in scenes that could easily go wrong, like the moment when she mortally embarrasses her son by asking if he needs condoms: "Protect and serve, it's my job." "The Fosters" also cannily incorporates features of the crime drama - a tense and surprisingly touching sequence involves Foster and her ex-husband, also a police officer, unexpectedly drawing their guns for an impromptu rescue - as well as the beach-party movie: the school where the other mom (Sherri Saum) works and all the kids study is literally on the beach, with surfers running into the water between classes. None of the actors playing the children jump off the screen, but they all do honest, unforced work, and Cierra Ramirez ("Girl in Progress," "The Secret Life of the American Teenager") is particularly good as the female twin, Mariana. In a promotional clip, Mr. Paige says that the show reflects "a very simple belief: that we're really, fundamentally, all the same." That kind of platitude indicates how disposable this kind of series can easily become; with luck, "The Fosters" will parlay its charming cast and spark of humor into something more. The Fosters ABC Family, Monday nights at 9, Eastern and Pacific times; 8, Central time. Produced by Nuyorican Productions Inc. and Prodco Inc. Created and written by Bradley Bredeweg and Peter Paige. Jennifer Lopez, Mr. Bredeweg, Mr. Paige, Elaine Goldsmith Thomas, Benny Medina and Greg Gugliotta, executive producers. WITH: Teri Polo (Stef Foster), Sherri Saum (Lena Adams), David Lambert (Brandon), Cierra Ramirez (Marianaa), Jesus (Jake T. Austin) and Maia Mitchell (Callie).