Away We Go, Sam Mendes, 98 mins (15)Cloudy with a Chance of Meatballs, Phil Lord & Christopher Miller, 90 mins (U)

Darling, we are going to have a beautiful little romcom

Sam Mendes's new film, Away We Go, has the most unlikely heroes imaginable: a solvent middle-class couple who don't break up, don't suffer any calamities, and who are not once involved in a bank robbery or an alien invasion.

Some viewers may well be nauseated by this solid partnership, especially when yet another acoustic pop ballad oozes on to the soundtrack, but when you consider how rare such specimens are in the cinema, the film seems positively radical.

Nor are Verona and Burt, played by Maya Rudolph and John Krasinski, entirely carefree. They're in their thirties and they're holding down decent jobs, but they still don't feel as if they quite belong in the adult world, a feeling that flares up when they discover, in a way that's hilarious, but not printable in a respectable newspaper, that Verona is pregnant. They expect Burt's family to be their support network, so they're floored when his parents (Jeff Daniels and Catherine O'Hara, a joyous double act) announce, three months before the due date, that they're about to fulfil a dream they've held in their hearts for decades: they're moving to Belgium.

Burt and Verona's response is to find somewhere new to live themselves. They decide to fly around the US and Canada, visiting old friends and relatives, to see which town might suit them, leading to a series of extremely funny encounters reminiscent of Flirting with Disaster and Broken Flowers. In Arizona, there's the raucously sozzled Allison Janney, who yells insults at her offspring, convinced that they're not listening anyway. In Wisconsin, there's Maggie Gyllenhaal, a New Age zealot who thinks that prams are a force for evil. "Why," she spits, "would I want to push my children away from me?" At first these episodes are played for laughs – and there are laughs aplenty – but as Away We Go progresses, its underlying concerns bubble to the surface, and they're remarkably adult for what appears to be a light comedy.

Few films would dare to be so candid when addressing death, fear, infertility, relationships with parents and children, and the havoc breastfeeding can wreak on a woman's embonpoint. The screenplay is by Dave Eggers and Vendela Vida, a pair of massively acclaimed novelists who happen to be married to each other, and their salty dialogue is so genuine that you'll feel as if you're eavesdropping. The film has more warmth and emotion in its little finger than every one of this year's romantic comedies put together.

Away We Go also deserves a prize for being one of the only films ever made about pregnancy which doesn't finish with a race to the maternity ward. In the closing scenes, Verona still hasn't had her baby, and still isn't sure whether she and Burt are living in the right place.

As cartoon plots become increasingly contrived (Bolt, Ice Age 3) and tortuous (Ratatouille, Wall-E), a film as straightforward as Cloudy with a Chance of Meatballs is something of a relief. It's that age-old story: boy invents contraption that converts water into food; boy becomes hero when hot dogs and ice cream rain down on his home town; boy battles to shut down contraption when town is hit by a typhoon of spaghetti. Young children will be able to follow it from start to finish, but adults aren't short-changed, either. If the plot is admirably linear, all the more time and trouble have been invested in the delightful characters, visual gags, and zinging dialogue that parodies disaster-movie conventions without playing Spot the Film Pastiche. My only reservation is that the tidal waves of nacho cheese and wobbling mountains of beef might put you off your dinner for days.

The heart-wrenching Birdwatchers is set in Mato Grosso do Sul, Brazil, where the dispossessed Guarani-Kaiowa people work in semi-slavery as farmhands, or dress up in feathers to give the tourists a thrill. It's excellent both as an enraging polemic and a novelistic ensemble drama.