Ten years ago, Jennifer Westfeldt launched onto the independent film scene as the co-writer and star of the hilarious sleeper hit “Kissing Jessica Stein,” an edgy film about a straight woman who surprisingly finds herself embarking on a same-sex relationship. Westfeldt has it all: looks, wit, comic timing, dramatic skill and writing chops. It’s a delight to see her back in action in “Friends with Kids” — a tamer concept with more mainstream appeal, but with the same clever writing for smart people about smart people, that’s both funny and emotionally resonant. “Kissing Jessica Stein” launched Jon Hamm’s screen career by giving him his first substantial speaking part; here’s hoping “Friends with Kids” will bring Westfeldt into the mainstream.

“Friends with Kids” is another predictable yet fresh story about how best friends — in this case, single, neurotic New Yorkers approaching forty, Jason (Adam Scott) and Julie (Jennifer Westfeldt) eventually find themselves realizing, after 20 years, that they don’t just have good banter but are also in love. All it takes is for them to decide to have a child together — as friends, committed 100 percent, half the time — to realize that they are soul mates in and out of the bedroom.

Jason and Julie, however, have watched their friends have kids and then turn into seemingly unrecognizable people. Their friends Leslie (Maya Rudolph) and Alex (Chris O’Dowd) have moved to lowly Brooklyn and seem to have become inexplicably mean. Missy (Kristin Wiig) and Ben (Jon Hamm), who used to be incapable of keeping their hands off one another, after having kids, now only resent each other. Superficially, at first, it seems to our rom-com stars that children ruin marriages.

There are a lot of laughs to be had as Jason and Julie decide and plan to conceive. They like to play a game of picking which death would be worse — by alligators or by shark — on the phone while in bed with other people. They comment, wittily, on all the absurdities of parenthood: that parents bring rowdy kids to $100-a-meal restaurants, never sleep and throw tantrums because of it and obsessively inform other people of their child’s progress, including their first successful visit to the toilet. Westfeldt, like Woody Allen, has a knack for accurately writing neuroses in a way that allows us to laugh at them, and Julie’s neuroses provide a lot of comedic material.

Jason and Julie’s child-rearing arrangement works in the beginning. They are great friends and can communicate healthily to share responsibility civilly and find a way to get sleep, eat and not turn their respective apartments into unlivable dumps. In one adorable scene, Jason comes downstairs in the middle of the night to feed the baby with breast milk from the fridge, helpfully labeled: “pure,” “one latte,” “one glass of wine” and “sushi for dinner.”

But of course, the pair starts to get jealous and has problems when they each meet a cute someone new: he the young in every way, lithe, gorgeous, but smart and quip-y Mary Jane (Megan Fox), and she the good looking, mature Kurt (Edward Burns). It’s around this time when the film shifts from a lightweight sitcom vibe to a more emotionally complicated place. On a ski trip, the non-couple is confronted with some difficult questions. How they are going to explain their situation to their kid, and handle his emotional response, once he is old enough to start asking questions?

This is dangerous territory because it draws attention to the plot’s flaws — the rash decision by smart people to have and share a child to suit their own sex lives with little regard for the child itself — but it succeeds at deepening the characters and their relationships. Though Ben seems to have become the cliché of the husband-turned-jerk, he is the one that starts asking these mature questions, albeit in a cruel and confrontational manner. The answers to these questions — and how this propels the story forward — reveal a lot about the characters and how our leads almost got things right. It forces Jason and Julie to deal with their issues, and the film earns the self-knowledge that these two achieve. Their friends’ relationships, which are first played for comedy — their fights and their lack of sex life — are deepened, and we see why one marriage failed and the other succeeded, despite both being grown-up partnerships of equals.

There seems to be a new trend in rom-coms to put smart characters in stupid situations, and yet end with the most modern, funny and poignant films as a result: “Juno,” “Friends with Benefits,” “Easy A” and now “Friends with Kids” all fit this bill. We need more contemporary stories like these to challenge conventional romantic narratives and stereotypes. Westfeldt has proven herself adept at telling these stories, writing characters with wit and vulnerability, and I look forward to seeing what she comes up with next; with any luck, it will be something a little more realistic, and we won’t have to wait another decade.