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Jennifer Garner loves one role the most: being a mother. While being an actor is her job, it's not at the top of her mind when she's running around with her two little girls and 5-month-old baby boy.

"It's just so shocking to have another one. Again and again, I say, 'Oh, the girls,' and then I think, 'The kids,'" she says. "It's just shocking that there's really a baby around and it's so -- I don't know. Maybe it's because it's my last, but I'm just so nuts about him."

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Garner says the message of her new film "The Odd Life of Timothy Green" -- which centers on a long-childless couple magically gifted with a 10-year-old son who spontaneously emerges from their garden -- appealed to her sensibilities as a mother. "It asks you to love the child that you have and not try to make them into something that they're not. It asks you to not judge yourself as a parent and to just be where you are, and to know that sometimes when you're trying your hardest you're screwing up the most," she says.

The actress admits that parenthood came quickly for her and husband Ben Affleck -- their first daughter, Violet, was born months after the star couple tied the knot in 2005. "I mean, Ben and I had said, 'Let's have a baby,' and we were parents before we even knew it," she chuckles. "We were just like, eight days later we were on our way." Violet was joined by sister Seraphina in 2009 and brother Samuel earlier this year, leaving Garner scant time to over-indulge in fantasies about what kind of mother she'd be and what kind of children she'd have. "My kids came out very clearly who they are, and that's fabulous," she says.

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Parenting is a learning process, she says. "It's just that now my kids are starting to be old enough that I can have a dialogue with them about it. I hope that they don't see me as perfect, and I hope that they know that I'm fallible and that I'll be responsible for what I screw up on - and that sometimes I can screw up and it's okay and they can deal with it," she adds.

As for what happens now with a full house and acting career? Garner says she just now starting to get used to the idea of going back to work.

"I don't have any jobs that I'm thinking about doing. I've been pushing that out of my mind, but maybe it's just doing hair and makeup and starting to do this stuff, like, I'm going, 'That's right. I knew that I was forgetting something. I'm an actor. I should act,'" she says. "But my baby is just five months old. You kind of come out of a fog around now, five, six months. I'm starting to be a little more open to it."