Life is messy, and one of the ways we try to make sense of it is through stories. With their selection of detail and events and resolution — whether a happy or a sad one — they give us a sense of structure and logic and catharsis. They help us sort through life’s ambiguities and complications, even if only for a couple of hours.

At least, that’s what stories do most of the time. Once in a while, they are content just to reflect back to us the very messiness and ambiguity we are experiencing. And when they do it well, they give us a sense of recognition that is in its own way cathartic. This film manages to do that and to be subtly subversive, lulling us across some of our own internal boundaries with its matter-of-fact portrayal of family life.

Nic (Annette Bening) and Jules (Julianne Moore) are a long-time couple who have each given birth to a child, biological half-siblings because both women used sperm from the same anonymous donor, selected as optimal on the basis of his profile. Now the children, Joni (Mia Wasikowska of “Alice in Wonderland”) and Laser (Josh Hutcherson of “Journey to the Center of the Earth”) are teenagers and curious about their biological father. So, without telling their moms, they contact him.

He is Paul (Mark Ruffalo), an organic farmer and restaurateur whose free-spirited approach to life is very appealing to two teenagers emerging from a home that is rather hot-housed by comparison. Nic and Jules have created a deeply nurturing, “Let’s talk about our feelings” environment that feels claustrophobic and intrusive to their children, especially Laser as the household’s only male. In a brief but beautifully filmed scene that opens the film, Laser looks on with a mixture of curiosity and longing as a friend casually roughhouses with his dad, captivated by this particularly male kind of communication. It may be in part this emotion that keeps Laser connected to a friend his moms correctly believe to be a bad influence.

Paul is an enticing figure for the teenagers, comfortable with his maleness and easy-going. And Paul himself is enticed by Joni and Laser, who surprise him with a sense of connection and stability he did not realize he was missing. Just as they are separating from overshare central in the house they grew up in as a normal part of adolescent search for identity, he is drawn to the road he did not quite realize he chose not to take. And this plays out in ways that threaten everything the family has built.

The title focuses on the kids, but the movie is really about the adults. The small miracle of this film is its portrayal of a long-term marriage, its perspective unadorned but sympathetic, satiric but tender. The dynamic of affection, distraction, familiarity, and frustration is deftly portrayed. The expectation of the movie is that audiences will take for granted that a same-sex relationship is just like every other relationship we have experienced and seen portrayed, and if there is any surprise at all it is how quickly we do.

And then, just as we get comfortable with the familiar discomforts of the relationship, it all gets turned upside down and we and the characters are asked to jettison yet another level of expectations and boundaries.

Bening and Moore are magnificent. It is a pure pleasure to see women with real faces on screen. They hold nothing back in allowing themselves to be seen fully in every sense of the term, opening themselves up with breathtaking generosity of spirit. The kids are all right in this film; the grown-ups are even better.