When I think of ideas rife with comedy, I think of double-fatality car crashes that leave infant children orphaned.

When I think of ideas rife with comedy, I think of double-fatality car crashes that leave infant children orphaned.

OK, maybe not, but this is the setup chosen for the new parenthood comedy "Life As We Know It." If you think that's a downer, don't worry. There are plenty of baby poop jokes.

Katherine Heigl and Josh Duhamel play two opposites thrust together into parenthood. They learn mutual friends left a will naming them as guardians of their infant daughter. Hilarity ensues.

"Life As We Know It" is a miserably bad idea on paper. It's actually slightly better on screen, but comedy is paired with a heavy love story and the movie never find a good balance.

In fact, Heigl's breakout film role in "Knocked Up" is a much better execution of this mix. And she was much funnier before she tried so hard to be America's sweetheart.

Duhamel was cast to make the female audience swoon, but his charming lout could've been funnier in more-skilled hands.

"Life" is a reasonably diverting date-night comedy, but it's not worth getting a babysitter for.