Joni (Mia Wasikowska) and her younger brother Laser (Josh Hutcherson) live in an attractive, upper-middle-class home with their parents — one a doctor, the other still searching for her niche. The doctor, Nic (Annette Bening), can be a bit of a pill, so it's up to the searcher, Jules (Julianne Moore), to take care of the nurturing. All in all, it's a happy family.

But Laser is curious about the sperm donor who helped make it all possible. So when Joni turns 18, she reluctantly agrees to look the guy up. His name is Paul (Mark Ruffalo), he has an organic garden and restaurant, and he's cool with just about everything.

It's not long before Paul and Nic confront the fact that their personalities clash. But in Jules, the easygoing gardener finds a kindred spirit — someone who's on the same loopy wavelength. It only makes sense for him to hire her as a landscaper. That's when the real trouble starts.

Directed and co-written by Lisa Cholodenko ("Laurel Canyon"), "The Kids Are All Right" takes a refreshingly matter-of-fact approach to its characters' sexuality. Far from being reduced to symbols of social change, Jules and Nic are simply — as Joni would say — "the moms." It's the freewheeling Paul who truly shakes things up, at a cost that some may find unfair.

Bening, who was impressive in the recent "Mother and Child," is at once brittle and brilliant as Nic. Moore deftly explores Jules' comic confusion without underplaying her despair. And Ruffalo hasn't been this good since his breakthrough role in "You Can Count On Me."

"The Kids Are All Right" probably could have used a few more scenes to come to an even more satisfying conclusion. But it's a terrific film anyway.