The 'Dukes of Hazzard' star, who has three-year-old daughter Maxwell and two-year-old son Ace with husband Eric Johnson, insists she has no plans to expand her family further in the future.
She said: "No more kids on the horizon. That would freak me out a little bit."
However, the 35-year-old beauty's decision may leave Maxwell disappointed as the youngster is "obsessed" with babies, in particular her aunt Ashlee Simpson's daughter Jagger, who was born in July.
Jessica told 'Entertainment Tonight': "Jagger just came over to see me, Maxwell and Ace the other day and she's so tiny and so sweet! And Maxwell is just obsessed! She has baby dolls, she wants to be a mom already. She's a care taker!"
The singer-and-actress also credits her kids for helping her stay in shape.
Asked how she keeps her trim figure, she said: "A lot of squats! A lot of push-ups, got to keep these things up. And running around with my kids. That is a diet in itself."
Though Jessica hasn't released new music since 2008, she hinted some new material may be on its way soon.
She teased: "I feel like I'm at such a comfortable place to like open my heart and share so much with everybody.
"So, music makes the most sense."