July 14, 2016 01:45 PM

Right after Shiri Appleby gave birth to her son Owen Lee in December, she didn’t really notice many differences between her son and her daughter Natalie Bouader, 3.

“The first few months, everyone was like, ‘Isn’t it so different?’ And I didn’t really understand,” Appleby, 37, told PEOPLE while celebrating Under Armour‘s debut of the UA Crossback Bra in West Hollywood, California, on Tuesday. “Then we just vacationed with some friends of ours that have a baby girl the same age, and she’s dainty and sits, and he’s really active. It’s much more energy!”

Six-month-old Owen, whom Appleby describes as a “very happy child,” has already hit a major milestone.

“We’re teething and eating solids,” she says. “Big things!”

Stefanie Keenan/Getty

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But Owen doesn’t have a favorite food just yet.

“We’re just kind of exposing him to everything right now,” says the UnREAL star. “We’re really just trying to create as wide a palate as possible.”

And big sister Natalie is fully embracing her new role. “She’s a big girl, she’s a big kid now, she’s really just taken to it,” says Appleby. “It’s really wonderful to see the two of them be together. It’s great.”

And while being a family of four — Appleby is engaged to her children’s father, restaurateur Jon Shook — is “a lot more moving parts,” it’s also a lot of fun too.

“Today we just went to the supermarket and bought a pizza. We came home and they wanted to make the pizza first thing in the morning,” the Roswell alum says. “Let’s do it!”

Despite having to juggle family and work, Appleby says fitness has been a priority for her lately.

“Taking care of myself and working out is something that I’ve really been focused on, because having to go to work and be a mom, I’ve noticed the one thing you don’t give yourself enough of is time for yourself,” she says. “And for me, that’s really working out.”

While on the set of UnREAL, Appleby works out before shoots.

“I do my hair in the morning really quickly, and then I use the other time to work out and do DVDs in my trailer,” she says. “I do the Tracy Anderson DVDs. I do 30 to 45 minutes maybe four days a week when I’m working.”

Now that the season has wrapped, Appleby is looking forward to getting back to her usual fitness routine.

“I’m going back to the gym now. I’m so happy!” she says, adding that her go-to workout is Pilates.

“It feels good to just work your core, work your arms,” says Appleby. “It really makes you feel strong and engaged in the world in a healthier way.”

Gabrielle Olya

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