Hilaria Baldwin Stars with Her Three Kids in Stunning Maternity Shoot: This Is a 'Magical Time'

"We make it fun — we don't have an agenda. The moment when I try to make my kids line up, which I will try sometimes, it never works out," soon-to-be mother of four Hilaria Baldwin (who's expecting a baby boy with husband Alec) tells PEOPLE of her family maternity photo shoot, sharing exclusive images from the ethereal session.

"Just playing ... capturing them in their element," she adds of Leonardo Ángel Charles, 19 months, Rafael Thomas, 2½, and Carmen Gabriela, 4½. "It's more about creating a relaxed environment."

While Leo is "too little to understand" the changes that are happening in his family, the 34-year-old yoga instructor tells PEOPLE, "It's such a magical time of waiting" while they prepare for the arrival of their newest member.

"It can be difficult in some ways, it can be uncomfortable in some ways, but it's this magical time, and capturing that each time around has been incredible because it goes so quickly," she says.

"The baby comes out and all of a sudden that belly starts to shrink, so it's been quite special," Hilaria adds. "Around our house, we'll frame a few of these photos from each of the maternity moments that we've captured."

"It's been interesting over the process of my pregnancy to watch Rafael start to understand there's a baby in my tummy," Hilaria tells PEOPLE of her older son. "I don't know if he quite understands it — the reality that's going to come."

She continues, "I don't think he remembers when Leo was born but he'll lift up my shirt and say, 'There's a baby in your belly. Baby, come out,' he'll talk to him. It's really sweet."

"Carmen understands it a little bit more," Hilaria says of her oldest child's reaction to her third little brother on the way.

"I love when she's nuzzled toward my belly — I feel like that's very her and she's very nurturing," continues the fitness expert.

Of her kids, Hilaria says, "Trying to get the three of them for a good photo ... Eroula, who takes the photos, is like a magician with them — she's really incredible."

"She's a Greek mama of three herself and she is just so good with them," she adds.

"It's my third boy in less than three years so there wasn't a lot to do," says Hilaria. "Hand-me-downs from my other children. I'm recycling the crib from before so it was a very easy thing."

"For me, who's such a nester, it was actually a little bit difficult because I want to do things all the time, so my entire family is annoyed with me that I'm constantly reorganizing everything," she jokes.

"The baby is very big — I was the genius who had kids with Alec Baldwin, who's a lot bigger than I am, so we're monitoring his size and I'm trying to stay as active as possible and encourage him out," Hilaria explains of her son on the way.

"I think it's any minute now, hopefully, but we're just keeping a close eye on him and watching this giant baby grow," she adds. "We always laugh — he knows he's the youngest of four, so he better come out when he's big enough to defend himself."