It would seem that Peet - who has appeared in movies such as Something's Gotta Give and The Whole Ten Yards - is aware that her biological clock is ticking and must consider the risks of conceiving past the age of 40.

There are many precedents for celebrities becoming moms at an older age - Kelly Preston is pregnant at 47 and Céline Dion is expecting twins at 42. However, Halle Berry - who gave birth to daughter Nahla in 2008 at age 40 - warns "don't look at celebrities who are doing it and think, Oh, it's easy. It's really not."

Dr Alan B. Copperman of Mount Sinai Medical Center points out some of the problems. "At 40 there is only a 10 percent chance of conception and at 45, it's just 2 percent." Add to that the often needed fertility treatments, preterm labor, dangerously high blood pressure and diabetes, and you can understand Ms. Peet's concerns.

Amanda recently said that Frankie is adjusting well to big sisterhood.

It's been good, she's a little more moody than usual but it's not directed at the baby. It's more like, 'Frankie eat your broccoli,' and she starts screaming. She wants to have a baby in her belly and she wants to breastfeed."

The mom-of-two made up for her last minute absence by appearing on the talk show earlier this week, though she clearly had babies on the brain.

Struggling to recall the plot of her new film Please Give,, Amanda said, "I have a foggy brain right now... Oh my gosh. I have no business being here!"

She had plenty to say when talk turned to her girls, though. Revealing that her 3-year-old daughter Frances Pen is still adjusting to being a big sister to little Molly June, she explained, 'It's been good, she's a little more moody than usual but it's not directed at the baby. It's more like, 'Frankie eat your broccoli,' and she starts screaming. She wants to have a baby in her belly and she wants to breastfeed."

Let's take a look at some other celeb sibling names. Whose names sound the best together?

Peet, 38, had been scheduled to appear on the Late Show with David Letterman on Tuesday night to promote her upcoming film, Please Give. But baby Molly had other plans!

Peet and Benioff, who wed in 2006, have a daughter Frances Pen, 3.

Congratulations to the Peet-Benioff family!

The 38-year-old Saving Silverman star has just returned from a trip to Berlin where she was promoting her new film, Please Give.

Amanda and her husband, screenwriter David Benioff, are expecting their second child - rumored to be another girl!

Please Give is a film about privileged New Yorkers ridden by guilt, costarring Catherine Keener and Rebecca Hall. The 60th Berlin International Film Festival runs until Sunday.

The gorgeous 38-year-old 2012 star and her husband David Benioff are expecting their second child. They are already parents to daughter Frances Pen, who turns 3 on Saturday!

Amanda is promoting Please Give, a film about privileged New Yorkers ridden by guilt, costarring Catherine Keener and Rebecca Hall. The Berlin Film Festival runs until Sunday.

The gorgeous 38-year-old actress and her husband David Benioff are expecting their second child. They are already parents to daughter Frances Pen, who turns 3 on Saturday!

Amanda and David are currently expecting their second child - rumored to be another baby girl!

Just over a week ago we spotted little Frankie having a fun playdate with Jason Bateman’s daughter, Francesca, 3, at Coldwater Canyon Park in Beverly Hills.

The day before, we spotted the adorable tot having a playdate with Amanda Peet's 2 1/2-year-old daughter Frankie.

Watch for Jason's upcoming flicks this year: The Baster, co-starring Jennifer Aniston and Paul, co-starring Seth Rogan.

The 2012 star and her husband, screenwriter David Benioff, are expecting their second child - rumored to be another girl!

We've spotted these two pals on a Hollywood playdate with their gorgeous girls, Frances and Francesca! So cute!

While at the Sundance Film Festival, Peet was overheard telling friends, "We're having a baby girl!" as she showed off her baby bump. The 38-year-old Something's Gotta Give actress and her husband David Benioff are already parents to daughter Frances "Frankie" Pen, 3 next month.

US magazine reports that the beautiful star, who was recently spotted at the Sundance Film Festival where she is promoting her new film Please Give, was overheard telling friends, "We're having a baby girl!" as she showed off her burgeoning bump.

Amanda, 38, is already mom to daughter Frances "Frankie" Pen, who turns 3 next month.

Last month, Amanda announced that she and her husband of three years, screenwriter David Benioff, are expecting their second child. The couple are already parents to daughter Frances "Frankie" Pen, 3 next month.

In 2007, the couple welcomed daughter Frances "Frankie" Pen, whom Peet named after her mother, Penny.

The 37-year-old 2012 star has been quite outspoken about childhood vaccines. "Frankly, I feel that parents who don't vaccinate their children are parasites." This controversial statement was later followed by a personal apology although she still strongly supports childhood immunizations.

Peet recently said it's important to take care of yourself in order to be a great parent:

You have to put your oxygen mask before you put on others’. It’s a good metaphor for parenting, but it’s really hard to do sometimes. A lot of women feel that if they’re exerting energy in different areas of their life or are really passionate about other things, it’s automatically detrimental to the child.”

Congratulations to the Peet-Benioff family!

On parenting her daughter Frankie: “You have to put your oxygen mask before you put on others’. It’s a good metaphor for parenting, but it’s really hard to do sometimes. A lot of women feel that if they’re exerting energy in different areas of their life or are really passionate about other things, it’s automatically detrimental to the child.”

On her work with Every Child By Two, a nonprofit group that strives to have all children vaccinated by age 2: "This is about children's health. This is about the future of our children's health. It's about what happens when you become complacent and you're not vigilant as a community. It's about the fact that I don't think parents feel like they're part of a community anymore. We all have to make."

"I have a daughter, and it helped to come to her after a day of filming one disaster after another because she was just wanting me to read The Cat and the Hat or whatever," Amanda tells Parade magazine. "That definitely kept me from getting too depressed. I'm trying not to think about what the world will be like when she grows up. I think more about when is she going to start drinking and wearing a g-string and how can I stop those things from happening."

Speaking of g-strings, Amanda also opened up about baring all on screen - and why she refuses to be a slave to the gym.

"I have an inner conflict. I'll be at the gym and I'll start thinking, 'What am I doing? I'm going to sag no matter what I do.' I've certainly taken my clothes off on camera, but you have body make-up and special lighting," she says. "I mean, someone with a figure like Jennifer Aniston has a trainer, a cook spinning out some version of the latest diet, and probably a stop at the tanning salon. Then teenage girls go, 'God, I wish I could look like that.' Maybe they wouldn't if they knew what it took.'"