J.Lo's 'What to Expect' Advice to Jessica Simpson

This week Jessica Simpson gave birth to a healthy, almost-10-pound daughter named Maxwell, and What to Expect When You're Expecting star (and mother of twins) Jennifer Lopez has some choice words of advice for the new star mom.

Related: Jessica Simpson Welcomes Baby Girl

"Well, she's going to be so sleepy," Jennifer tells ET's Steve Jones with a knowing laugh. "Hopefully her man is helping her out a lot and they can balance that. It's a magical time. When that baby's first born, it takes over your whole life. Just enjoy it. Just enjoy every second. It just goes so fast. Mine's this big now, I feel like I had them yesterday."

Video: Expect Laughs from Elizabeth in 'What to Expect'

Jennifer stars alongside an all-star cast that includes Elizabeth Banks, Cameron Diaz, Brooklyn Decker, Chace Crawford, Anna Kendrick, Matthew Morrison, Dennis Quaid, Rodrigo Santoro, Ben Falcone and Joe Manganiello in the family comedy inspired by the well-known New York Times bestselling pregnancy manual.

Video: Expect the Unexpected in 'What to Expect' Trailer

In theaters everywhere May 18, What to Expect When You're Expecting chronicles the hilarious and heartwarming stories of five couples who face the many challenges adjusting to pregnancy and parenthood.

Watch the video to find out if Cameron Diaz and Matthew Morrison would like to have some children of their own, and Elizabeth Banks and Ben Falcone's tips for new parents.