Raising kids is tough, especially when they're not yours.

"Life as We Know It," which opened Friday, is one of a long line of romantic comedies about single people becoming parents for the first time. Katherine Heigl and Josh Duhamel play two free spirits who become reluctant caregivers to a baby girl when their mutual best friends are killed in a car wreck (a common death in this genre).

Here's a look at some other first-time parents:

"About a Boy" (2002): Hugh Grant is his charming stuttering self as a wealthy bon vivant who pretends to have a son to impress women. He ends up befriending a single mother (Toni Collette) and her 12-year-old son. The guys bond over buying shoes and keeping bullies at bay. It's one of Grant's best roles.

"Baby Boom" (1987): Corporate big-shot J.C. (Diane Keaton) sees her world turned on its head when she inherits an adorable baby girl from a distant relative. Her maternal instincts eventually kick in, and she gets Sam Shepard as a reward for her lack of sleep and spit-up on her suits.

"Big Daddy" (1999): Like Grant, Adam Sandler adopts a kid to impress his girlfriend. Scary thought. But his puerile imagination comes in handy. Telling a kid to wear a pair of "magic sunglasses" to make him invisible and ease his anxieties is genius.

"Martian Child" (2007): A widower/sci-fi writer (John Cusack) decides to adopt a 6-year-old boy who thinks he's from Mars. At least the tyke is low-maintenance, preferring to shield himself from sunlight by hanging out in a box.

"No Reservations" (2007): After her sister dies in, yes, a car wreck, a hardened New York chef (Catherine Zeta Jones) is in for a challenge when her niece (Abigail Breslin) comes to live with her. Aaron Eckhart helps her in the kitchen and elsewhere.

"Raising Helen" (2004): After her sister and brother-in-law die in yet another car wreck, a high-powered fashion exec (Kate Hudson) takes in their three kids (Abigail Breslin, again). While most men might run for the door, John Corbett is up for the surrogate dad job. Well, if you look like Hudson, anything is possible.