"After having kids, I don't think that your hips really ever go completely back," Jessica Simpson said

Jessica Simpson is opening up about how her body has changed after three children.

The star, 39, showed off her latest collection from her clothing line with mom Tina on HSN Thursday, during which she talked about her post-baby figure after giving birth to daughter Birdie Mae in March.

“It’s been a lot of hard work, I’ve been working very hard,” Simpson said about losing 100 lbs. after welcoming her now-6-month-old baby girl.

“When you’re pregnant, I gain a lot, I mean, a lot. I didn’t expect to gain as much with my third,” the mom of three said. “I thought I’d learned my lesson, but apparently, that’s just the way God made me, very hungry and pregnant.”

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Jessica Simpson
Jessica Simpson and daughter Birdie
| Credit: Jessica Simpson/Instagram

And while discussing her latest flared jeans, Simpson revealed that she has shifted her closet must-haves for her body type.

“I don’t think I’ll ever get back to [my skinny jeans]. I save them and say, ‘One day,’ ” she said. “But after having kids, I don’t think that your hips really ever go completely back,” she added. “Your body changes!”

In addition to talking about her body after baby, Simpson raved about how her two older kids — son Ace Knute, 6, and daughter Maxwell “Maxi” Drew, 7 — have taken care of their little sister.

“They’re great with Birdie,” the proud mom said.

Jessica Simpson
Credit: The Image Direct

However, returning to work and leaving Birdie at home also made Simpson miss a big milestone recently.

“I went out of town for two days and now she’s eating carrots,” she said. “Pureed, of course, but she got to eat her solid food and she’s loving it. Her first solid food.”

Simpson recently told her fans and followers that she’s “so proud to feel like [herself] again,” sharing that she had lost 100 lbs. since giving birth and had previously “tipped the scales at 240.”

A source told PEOPLE that Simpson has been “very committed” to the fitness process.

“She’s working hard and working out and eating healthy and trying to get back in her best shape and excited for what’s ahead,” the source said of the star, whose upcoming memoir is set to be released on Feb. 4.

“She’s trying to get back to her healthiest place. And she just wanted to get to a place where she feels her healthiest. She’s not focused on the number, but on feeling her best self,” the source added.