“I think they’re going to be great parents,” Cavallari, 30, told PEOPLE. “I think they have a very solid foundation, which that’s what it’s all about.”
The fashion designer and author adds with a laugh, “I think that they’ve survived a lot together, so I think having kids is going to be a cake walk for them.”
On Tuesday, Heidi sweetly thanked her husband on social media “for the best gift … a baby” in celebration of their eight-year wedding anniversary. The pair, who tied the knot in April 2009, are expecting their first child in October.
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“Heidi, she’s so funny,” Cavallari says of the expectant mama. “She was asking my opinion about baby names, which is so sweet.”
“I gave her a whole list of different items that I loved as a new mom,” continues the mother of three. “And I’m just so happy for her because she’s been wanting a baby for so long, so it’s a very exciting time.”
“[There’s] something in the water!” teases Cavallari. “It’s really funny that everyone is having babies at the same time. What are the chances? It’s pretty hilarious.”
And even though there hasn’t been any talk of planning one big baby shower for all The Hills ladies, Cavallari says a reunion “would be fun.”
“It’s so tough with everyone all over the place,” she explains. “Audrina invited me to her shower and I just couldn’t get there, but I would love to see them, so we should figure something out.”
When it comes to parenting advice for all the first-time moms, Cavallari — who jokes she’s “an old pro” — says her advice is “universal for anybody.”
“It’s that listen to advice, but ultimately do what’s best for you because every family is different,” she shares. “Every child is different. You cannot parent all of your children the same way because once you have kids you realize the nature-versus-nurture thing.”
“Kids come out who they’re going to be,” she continues. “I definitely think environment plays a role, but I think the core of who you are, you are born with. And so you as a mom are the only one who really knows your child and knows what’s best for your child.”
Despite the Hills baby boom, fans shouldn’t expect Cavallari and her husband Jay Cutler to be next. “I’m done,” she admits. “Three is plenty. I am done.”
Explains Cavallari, “We just feel like a very complete family. I can’t imagine having another one and rocking the boat. I don’t want to go back to the baby phase, to be completely honest. The baby phase is tough.”
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Right now, Cavallari is focusing on getting 17-month-old daughter Saylor James out of diapers, which she says should happen in about six months.
“I’m really looking forward to putting away that Diaper Genie and never getting it out again,” she adds with a laugh.
And along with growing out of diapers in the near future, Cavallari’s baby girl is also “starting to talk.”
“[It’s] not much,” says the former reality star. “But she’s saying a few things. Her big thing right now is going, ‘Bye! Bye!’ She’s just getting so big.”
“We’re going to have a little birthday party for Jaxon with his buddies from school,” Cavallari says of her younger son. “It’s at this place called The Blast Zone and they have the big trampolines and the foam pit and the kids can just run around,” she continues. “It’ll be fun [and] just easy.”
“Camden was like, ‘Why are we not moving to L.A.?’ ” Cavallari says with a laugh. “I’m like, ‘Ask your dad.’ ” (Cavallari famously grew up in Laguna Beach, California, and lived in Los Angeles after graduating high school.)
And with three little ones, Cavallari credits her former Chicago Bears quarterback husband to being able to strike a balance. “I’m lucky because Jay is home all the time, and so he helps a lot,” she says. “He’s a very hands-on dad.”
She continues, “It’s sort of worked out the last few years that during the football season, I don’t work as much — I’m home a lot more. And then once the off-season rolls around, that’s when things for me start picking back up.”
Along with Cutler, 33, Cavallari’s mom and mother-in-law also lend a hand with babysitting.
“Family helps a lot,” she shares. “And I have a nanny [who] comes in the mornings five days a week. She’s awesome. She allows me to be able to take my boys to school and then go work out and get some stuff done in the morning if I need to.”
And although Cavallari was only apart from her babies for 24 hours on Thursday to attend the launch of her new jewelry line Uncommon James in West Hollywood, California, the star admits that after “even just one full day of not seeing” her kids, much more time than that seems to have passed when she gets back home.
“It’s like, ‘God, you guys have grown up just within that one day I didn’t see you!’ ” she says. “It’s crazy.”
Uncommon James’ debut collection is available online now at uncommonjames.com.