The 41-year-old actress, who has kids Violet, eight, Seraphina, five and 23-month-old Samuel with husband Ben Affleck, was still nursing her young son during the shooting of the biographical drama film, reported Contactmusic.
"I was very nervous - it's hard to leave your baby at home and go to work. And I was a nursing mum, so I was extra emotional about it. I've nursed each of my babies and I've worked during that first year of having them," Garner said.
"If we talk brass tacks here, I'm versed in how to say, 'In about ten minutes I'm going to need to disappear', but on this movie we moved so quickly, there was never time. Everyone had to sit and wait for me, I hated making a crew wait, but I couldn't start weaning my baby just because of a movie," she added.