Why let a little thing like having a baby dampen your va-va-voom? Jennifer Garner gave birth six months ago to a son, Samuel, her third child with birthday boy Ben Affleck. Most new moms are uncoiffed at best, living in sweats at worst.

But not Garner. The 40-year-old Odd Life of Timothy Green star — who was born in Texas but raised in West Virginia — exuded radiance and vitality in a sexy dress and pumps on her Miami stop at the Four Seasons Hotel Miami Monday.

It helps that she loved the character she plays in the film: an infertile woman who, along with her husband, is able to conjure the child of their dreams in their garden.

How did you get involved in this project?

I begged [director] Peter Hedges to let me do it. I loved Peter as a screenwriter [ About A Boy], as an author [ What’s Eating Gilbert Grape?]. He has an in on whatever it is that makes people tick in relationships. He gets it right in the parenting aspect, the marriage, even sisters.

How was the chemistry on set?

We all had a great time. It’s just a real group of actors. There were no kind of huge movie stars. Ron Livingston is so dry, and every time he would walk on we would laugh. His wife Rosemary Dewitt plays my sister. When we were together, Peter would say, ‘OK, girls, let’s get to work,’ because we had so much to talk about.

Did you feel maternal?

You can’t be with a child for three months’ straight and in some way not take care of them. CJ Adams [ Dan in Real Life] plays Timothy. His mom was off screen the whole time, but I was there on set with him. I’d be like, “Do you need a snack? Do you have to go to the bathroom? Are you getting tired?”

If you could have made a list for what you’d want in your own kids, what would you have put down?

If I could go back in time when I was pregnant with my first child [ Violet, 6], which seems like a thousand years ago, maybe. Now that I’ve had three, the only thing that does matter truly is their health and their happiness and their safety.

Your character gets overprotective when Timothy meets a girl. Any parallels?

I was more protective of my first than I certainly will be of my third. I’m pretty crazy about this baby right now. I can’t imagine him growing up and loving anyone nearly as much as he loves me! But I’m a long way from that.

Does the movie bring infertility and adoption issues to the forefront?

There’s a lot of stuff that’s incredibly relatable. The town is going through a recession, their manufacturing jobs are leaving, there’s infertility. It’s all family stuff cobbled together, and they make it work.

You seem to be doing it all, fabulously. Have any advice for working moms?

Don’t put so much pressure on yourself. I’m working and not with my kids today, and it’s OK. My husband is sugaring them up, letting them watch TV, which is something I would never do in the middle of the week [laughs]. Just be where you are, forgive yourself and take it easy.

Madeleine Marr