"There are some incredible women whose bodies just, no matter how many babies they have they bounce right back to that slim-hipped, no stomach – I mean, it's incredible, I have so many girlfriends who have that physique and I'm so happy for them," the Alias star said.
WATCH: Jennifer Garner's show-stopping quarantine video is sure to go viral
However, she admitted that this hadn't been the case for her, adding: "I can work really hard and I can be really fit and I will still look like a woman whose had three babies and I always will."
The star said that some people still questioned whether she was pregnant, and explained that an appearance on the Ellen DeGeneres Show was an attempt to "take the bull by the horns."
Jennifer also recounted a deeply embarrassing moment when a "dear friend", who was visiting her in hospital after she'd given birth to her first child asked: "Is there another one in there?"
Although the incident didn't affect the actress too much, she said: "Luckily I have a sense of humour and I laughed but I remembered it, you know? I remembered it."
The star has three children
The 13 Going on 30 star also spoke about the close bond she has with her children, revealing that she's like a 'Coach Mom' to them.
"I just put them in the back yard, and I make them do 20 jumping jacks and I put on loud music and I make them run wraps around the little yard and I make them do sit-ups and hold a plank, just for fun before bed," she explained.
She added that one year her children decided to be 'Coach Kids' to her, joking: "I almost didn't survive it!"
The star also opened up about getting her first piercing at the age of 48, explaining that "Garner girls did not get their ears pierced" owing to their father's "strict and very conservative" views.
Jennifer spoke about being a 'Coach Mom' to her kids
Thankfully, she got a positive reaction from her father, telling Giovanna: "I mean, I'm 48 and I called my parents and said 'Dad, I'm going to pierce my ears' and he said 'ok Jennifer.'"
The star recently shared her pain at seeing how the ongoing coronavirus pandemic has affected the lives of her three children.
She shares her children, Violet, Seraphina and Samuel with, with her ex-husband Ben Affleck.
In an interview with ETonline, she said: "We've had to watch our kids be heartbroken and miss out on things.
"Which is one thing to miss out on something as an adult, but to watch your kids have to miss something they've looked forward to or to just see how isolated they are and on Zoom everyday…"
Read more HELLO! US stories here
Like this story? Sign up to our newsletter to get other stories like this delivered straight to your inbox.