It doesn't matter how strong-willed or independent-minded a person is; the moment he or she becomes responsible for another living human being, everything changes. Sometimes for the better, but not always. No, not always. The intricacies of parenthood, from the different ways it can alter relationships to the strain of dedicating the bulk of one's every waking minute to another, is at the center of "Friends with Kids," the attentive directorial debut of screenwriter-actress Jennifer Westfeldt (2002's "Kissing Jessica Stein"). An ensemble romantic comedy with a killer cast but not much in the way of a major driving plot, the film takes its time finding the right footing and momentum as the timeline drives furiously forward. Its limited scale and verbose banter sometimes threaten to remind of a small-screen sitcom, blessedly minus the laugh track. Then it sneaks up on you, the characters growing deeper and more real as their wholly believable situations take on a poignant life and immediacy of their own. Set in a bustling Manhattan metropolis of glittering skyscrapers, chic restaurants, varied culture and overpriced cab rides, "Friends with Kids" ultimately feels like vintage Woody Allen, and that's a very good thing, indeed.

Serial bachelor Jason Fryman (Adam Scott) and unlucky-in-love Julie Keller (Jennifer Westfeldt) have been strictly platonic best friends since college. Now in their late-thirties and with few romantic prospects before them, Jason and Julie yearn to be parents, but see how having children has turned their married friends—Leslie (Maya Rudolph) and Alex (Chris O'Dowd), as well as Missy (Kristen Wiig) and Ben (Jon Hamm)—into snippy, overworked, perpetually exhausted versions of their former selves. Looking to dodge this trap, Julie and Jason decide to have a baby together, splitting the demands of parenting right down the middle without having to worry about keeping an intimate relationship alive. It doesn't hurt that they live down the hall from each other in the same apartment building. The arrangement seems to work splendidly at first, with their young son seeming happy and well-adjusted as he grows from infant to toddler. In the interim, Jason falls for vivacious young actress Mary Jane (Megan Fox) and Julie is delighted to meet a kind, handsome, put-together divorcée, Kurt (Edward Burns). So far, so good, but despite Jason and Julie claiming that they aren't physically attracted to one another, it's a declaration they protest too much. Pretty soon they will have to face their complicated feelings head on—feelings that, once out in the open, could either make them stronger or tear them apart.

"Friends with Kids" begins with a brief glimpse of Jason, Julie and their pals sitting down to a nice dinner at a swanky restaurant. Missy and Ben have just returned from the restroom where they were doing more than powdering their noses. At a nearby table, parents have brought along a screaming child. "Is that even allowed here?" Jason and Julie question. Leslie and Alex, meanwhile, have an announcement: she's pregnant! Following the congratulations, Leslie and Alex make it clear that having a kid is not going to change them, and they certainly won't be bringing their little one to a nice restaurant to ruin everyone else's meals. Four years later, they've probably broken this vow. Leslie and Alex are constantly harried with their two kids, bickering over the smallest of things. Missy and Ben, also now parents, can barely stand to be in the same room together, keeping their sheer unhappiness not-too-covertly hidden away. "Our friends got mean!" Julie confides in Jason after a birthday get-together. Convinced that it isn't their kids who are at fault, but the people raising them who couldn't manage to hold onto the spark of their marriages, Jason and Julie decide to diverge from such pitfalls. By not being committed to each other beyond being good parents, perhaps their unconventional brand of parenthood is the answer to avoiding disappointment.

Following an opening half-hour that takes its time finding its groove—this may have something to do with the narrative zippily moving forward in time with almost each new scene until Julie's and Jason's baby son Joe is born—"Friends with Kids" settles effortlessly into its groove as a whip-smart dialogue- and character-centric human comedy. Produced independently before Lionsgate and Roadside Attractions picked it up for distribution, the film plays to its own drummer—that being triple-threat Jennifer Westfeldt—adhering to while twisting the commonplace practices of the romantic genre. Even if the viewer knows what will eventually happen between Julie and Jason, for once the getting-there doesn't test one's patience because it's so natural and uncontrived. There's also more going on beneath the surface than meets the eye. The film's strongest scene—a New Year's Eve ski getaway to Vermont that gets really real at dinner when Ben suddenly interrogates and criticizes Julie and Jason's nonconformist situation before Jason turns things around and forces him to examine his own faltering marriage to Missy—is supremely uncomfortable and impossible to tear your eyes away from, a tour de force of writing, performance and editing that should safely put a lump in every viewer's throat. This scene is crucial in putting an unwanted but much-needed magnifying glass on Ben and Missy, but also important because of the passion with which Jason speaks of Julie and the parenting decisions they've made.

Jennifer Westfeldt might be accused of a little egotism by casting herself in the lead role of a film she has also written and directed, but if it worked for Woody Allen, it certainly works for her. Westfeldt and co-star Adam Scott (2011's "Our Idiot Brother"), as tight-knit friends and eventual co-parents Julie and Jason, are a dynamic, delectable pair, easy to watch apart but all the better when they're playing off each other. The rest of the cast are truly in supporting roles, at times close to peripheral, but they each add texture and depth to the film's themes. Four "Bridesmaids" alums co-star as the friends with kids in question—Maya Rudolph (2010's "Grown Ups") and Chris O'Dowd (2010's "Gulliver's Travels") as frazzled but in love Leslie and Alex, and Jon Hamm (2011's "Sucker Punch") and Kristen Wiig (2011's "Paul") as Ben and Missy, a once-passionate couple whose marriage has crumbled since the moment they brought a child home from the hospital. It feels like Wiig is underused for the bulk of time—she seems distant and quieter than the rest of the characters—but eventually it is revealed that there is a reason for this in a sequence of bitter, piercing power that Wiig delivers brilliantly without barely having to utter a syllable. As an actor, she's the real deal, an eclectic phenom who can be screamingly funny, yes, but also heartbreaking. As Jason's new girlfriend, the gladly childless and younger Mary Jane, Megan Fox (2010's "Jonah Hex") is as relaxed as she's ever been on screen; of all her movies, this is the very first one that provides concrete evidence that she is—or can be—a fine actress. And as Kurt, Edward Burns (2012's "Man on a Ledge") is disarmingly pleasant, the kind of handsome, nice guy that could make it difficult for a person to be honest with themselves about having stronger feelings for another.

There is a small but unforgettable moment in "Friends with Kids" where Julie drops her son off at her mom's (Lee Bryant) house so that she can babysit him. Julie is taken a little aback by her mother expressing her wish to be closer to her grandchild, and then left touched when she sees her point out to the little one that "you are your mama's baby, and your mama is my baby." Putting into perspective the cyclical nature of life as it pertains to passing generations, the film sees Julie and Jason as another wheel in the cog, bucking the system with their interpersonal set-up but, as with most any parent, wanting the same thing as any parent: being the best they can to their child. Jutting away from too many predictably orchestrated conflicts and going for a more authentic atmosphere, writer-director Jennifer Westfeldt has made a bewitching romance about more than a boy and a girl, and a drama about rearing kids that goes blessedly beyond the black and the white.