Jessica Simpson Jokes She and Husband Eric Johnson 'Always Practice' Making Babies! (Exclusive)

The fashion designer and mother of two opened up to ET about the possibility of expanding their family, and dishes on how they keep their spark alive.

Jessica Simpson and husband Eric Johnson are the parents of two adorable children, but the proud mom says she still feels like she's got "baby fever" from time to time.

ET's Brooke Anderson caught up with the fashion designer at the Jessica Simpson Collection fashion show at Dillard's in Nashville, Tennessee, on Saturday, and she opened up about the possibility of expanding her happy family.

"My daughter is about to turn 6, May 1st is her birthday, and my son is going to turn 5 on June 30th and it's just like, 'Wait, so this is no longer toddler, this is full-on kid,'" Simpson, 37, shared. "My daughter [aready] thinks she's a teenager. My son at least wants to be a baby still."

Simpson and Johnson -- who began dating in May 2010 and tied the knot in July 2014 -- welcomed their little girl, Maxwell, in May 2012, followed by their son, Ace, in June 2013. 

Despite feeling a desire to have another baby running crawling the house, Simpson says she and Johnson "don't really know" if they'd like to have a third.

"We always practice," Simpson quipped. "But it would definitely have to be a miracle."

Simpson, who admitted that she makes no secret of the fact that she is "very attracted" to her handsome husband, also shared the couple's secret to keeping things "spicy" in their relationship: alone time.

"Today, we got to go on this trip without the kids, [and usually] we don't go places without the kids," she explained, adding that making the trip by themselves allows the pair to give each other "all of the attention."

As for expanding her family, Simpson seems to be more open to the possibility than she was last May, where she got very candid during her appearance on The Ellen DeGeneres Show about not wanting another kid.

"I'm not pregnant," the singer said, addressing speculation at the time that she might be expecting. "We got an IUD, nothing's gonna get in that uterus. I have two beautiful children and I'm not having a third."

To be fair, Simpson's two kids provide more than enough cuteness for one family -- especially with her daughter's adorable fascination with becoming a runway model.

At the Jessica Simpson Collection fashion show, the proud mom also opened up to ET about how her little girl already knows how to walk a runway "better than her mama!" Check out the video below to hear more.