"We're very happy as a party of five, but you never know," Vanessa Lachey tells PEOPLE about possibly having more kids with husband Nick Lachey

Vanessa Lachey isn’t turning down the idea of adding another little one to her family of five.

While the actress and her musician husband Nick Lachey are already parents to sons Phoenix Robert, who turns 3 on Christmas Eve, and Camden John, 7, plus daughter Brooklyn Elisabeth, 5 next month, Vanessa tells PEOPLE that “you never know” what might happen when it comes to having another child.

“The train of life is not stopping,” the mom of three says. “And what I mean by that is my kids are only getting older and more crazy every single day and more loving and more everything.”

Though Vanessa, 39, says her family is “so good and fulfilled with our crazy little three,” she reiterates that having another baby isn’t out of the question.

“Look, I always say that you never know. We planned on two and I always wanted three, but Phoenix was a surprise for us and the best surprise I could have ever asked for,” she shares with PEOPLE.

“We’re very happy as a party of five, but you never know. The second I say no, I’ll probably get pregnant. And the second I say yes, I probably won’t,” Vanessa jokes.

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Vanessa Lachey
The Lachey family
| Credit: Vanessa Lachey/Instagram

The TV host says that she feels “very lucky” that she and her 98 Degrees singer husband, 46, were able to have their kids, especially as she has “learned in this day and age, how hard it is for so many families to have children [biologically] or even to adopt children.”

However, her response to a scenario in which she were to be pregnant again is, “If it happens, it’s going to be not only the icing on the cake,” she tells PEOPLE, but “the cherry on top.”

In spending time with her little ones, Vanessa has been nurturing their “excitement for reading” with Epic!, a children’s reading app. After realizing what a “game-changer” the app was, she partnered with Epic! to help encourage other families to use reading as a way to spend time together as a family.

“I didn’t know about it before this year and am excited to spread the word because more people should know about it,” Vanessa tells PEOPLE.

Vanessa Lachey
Vanessa Lachey and son Camden
| Credit: Epic!
Vanessa Lachey
Vanessa Lachey and son Camden
| Credit: Epic!

“I love seeing my kids get excited about reading something that sparks their imagination,” she adds. “It’s something in terms of a hobby that is, I think, beneficial in multiple ways, and also it’s like a downtime.”

Vanessa explains that Epic! is the perfect “win-win” situation when it comes to balancing screen time and picking up a physical book.

“You get a little bit of screen time because it is like looking at a tablet or iPad or whatever device you have, but it’s also the book,” she says, adding that the app “gets [her kids] excited.”

“I’m actually embarrassed,” Vanessa laughs of not knowing about Epic! sooner.