Lauren Conrad Talks Becoming a Mom at First Red Carpet After Baby: 'It's the Best and Hardest Thing You'll Ever Do'

It’s been only nine weeks since Lauren Conrad and her husband William Tell welcomed their baby boy Liam James, but The Hills alum admits it’s crazy how much their little man has already grown.

“It’s insane!” the new mom told PEOPLE Wednesday at Beauty & Essex in Los Angeles during a “Girls Night Out” cocktail event to celebrate her new Kohl’s LC Lauren Conrad Runway + Plus Size Collection — Conrad’s first red carpet appearance post-baby.

“I took a photo of [Liam] yesterday,” says Conrad, 31, adding with a laugh, “I’m trying to take a monthly photo — all of the good moms do it — I’m really trying. So I took it and I looked at it next to his 1-month photo, and he had just changed. Like he was a completely different baby, and I was like, ‘Oh my God.’ ”

But Conrad admits it’s “good” to feel that way. “I think that you can become a little overwhelmed, just being at home with your baby all day,” she explains. “But seeing how fast they change, you realize it’s so important not to miss anything. It almost makes it harder to leave them.”

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And although she spends all of her time with her bundle of joy, the designer, author and lifestyle expert stepped out for a bit to celebrate the launch of her new collection while Liam spent time at home with her lawyer husband — who, according to Conrad, has been a super hands-on dad.

“He’s great,” she shares of Tell, 37. “He’s not afraid of babies, which is really helpful. He was 11 when his younger sister was born, so he has a lot of experience with babies. So that was really nice. He had way more experience than I did.”

As for how it’s been to experience being a first-time mom? “It’s been great!” says Conrad. “Honestly, it’s exactly as everyone describes it. It’s the best and hardest thing you’ll ever do.”

She continues, “It’s amazing. You fall so in love with your tiny person — it’s a whole new life.”