Knocked Up arrives just in time for summer, when everyone needs a good R-rated romantic comedy, except perhaps the kids, who would enjoy it if they could get in. The two children in the film, Iris and Maude Apatow (the director's daughters) steal all their scenes, and epitomize the knowing yet sweet sensibility of the film. After a somewhat predictable opening, with five stoner guys goofing around in their backyard and then in an amusement park, we meet Alison (Katherine Heigl) and those wonderful little girls, her nieces. As she drives them to school, the eldest, Sadie, and her little sister, Charlotte, argue about whether to listen to Rent or Green Day, and then, out of nowhere, Sadie informs Alison that she googled "murder." It's unexpected dialogue like this that makes Judd Apatow's new movie even better than his sleeper hit, The 40 Year Old Virgin. Like Virgin, Knocked Up finds humor and pathos in sex, friendship, relationships and the relentless process of growing up, but here the emphasis is on family, or at least the idea of family.

As anyone who has been to the movies lately unfortunately knows (trailers give away most plots, and nearly all the best lines), Ben (Seth Rogen) unintentionally knocks up Alison on their first date. They're the classic odd couple. Alison is blonde, ambitious and responsible; Ben is a good-natured, boyish, overweight slacker. They meet at a club where Alison is celebrating her on-camera promotion at E! Entertainment Television. In one of the film's best edited and funniest scenes, they drink, dance, drink, dance, with accelerating hilarity, until they wind up in Alison's bed. A drunken misinterpretation of "Just do it already" leads to a condom malfunction, and two months later Alison is calling the one-night stand she could barely stand the morning after. (Apatow captures Alison's sober assessment that morning by cutting from Ben's naked, doughy butt to Alison's disgusted face, in a characteristic gross/cruel/honest/funny observation.)

The two try to make a go of it as the pregnancy proceeds, but Alison fears winding up like her disgruntled sister, Debbie (Leslie Mann), and her detached husband, Pete (the reliable Paul Rudd), whose criticisms of each other, though highly entertaining for the audience, are hardly inspirational, as when Pete describes marriage as an unfunny "Everybody Loves Raymond" which goes on forever. Mann, Apatow's wife and the mother of Iris and Maude, nails her role as a nudgy, wacky wife and big sister. She's especially funny and fearless when she's confronting a bouncer who won't let her and her pregnant sister into a trendy club. (The bouncer's response is even better.)

It's no secret that Heigl is a gifted and beautiful comedic actress, and she's wonderful here, but Rogen, of The 40 Year Old Virgin and Apatow's "Freaks & Geeks" TV series, with his unabashed paunch, curly mop and scraggly beard, is a surprisingly lovable romantic lead. His rich voice is equally good at conveying a laid-back "Sweet" as it is a profane tirade, as he does later in the film when leaving a message for the couple's suddenly out-of-town gynecologist. While he and Heigl share less chemistry than Heigl and her "Grey's Anatomy" co-stars, they make a good team, especially when they're at each other's throats.

Apatow writes great fights, and all his players deliver them with relish. In one particularly juicy diss-fest, Ben laces into Pete, blaming him for his romantic problems, while Pete holds his daughter's birthday cake. After Ben storms out, Pete stands alone in the kitchen with a blank expression on his face, holds a beat, then walks into the party singing "Happy Birthday" as if nothing had happened. It's one of the movie's best moments, with its sure comic timing and wit. While many comedies mine the "Men Are From Mars, Women Are From Venus" viewpoint, not to mention the Peter Pan syndrome, few directors seem to enjoy this material as much as Apatow.