Maxwell and Ace can be very persuasive!
A source tells ET that Jessica Simpson's two kids, 6-year-old Maxwell and 5-year-old Ace, have been a "huge part" of her journey to baby No. 3 -- and may have inspired their parents to expand their family.
"Around Christmas last year she confided in close friends that both of her kids wanted a little sister or brother. She laughed about them putting the pressure on. Jessica also admitted she missed having a little baby and wanted to have more," the source says.
ET's source says that Simpson and her husband, Eric Johnson, are "truly wonderful parents" who have always talked about wanting a big family, and now that she's pregnant with her third child, the fashion designer is "bursting with joy."
"Jessica was very hush hush about her pregnancy, and even waited to tell some of her family and friends... Everyone knew how much she wanted this baby," the source reveals, noting that the Dukes of Hazzard star is especially thrilled to be having a baby girl.
"It's a fun reminder of the first time around. Of course, Jessica's a fashion mogul and has always said, there is nothing more fun than dressing a baby girl," ET's source says. "The kids are already helping plan the nursery. Especially Maxwell who is so excited to have a little sister."
Ace has also been expressing his input throughout this next stage in the family's life. "Her children have been a huge part of the decision in the entire process. Jessica and Eric are very dedicated parents and rarely do things without their kids. They have such a close-knit family," the source reveals, adding that Simpson's father, Joe, and her sister, Ashlee Simpson Ross, are also a big source of support.
"Jessica's father, Joe, is also very involved in his grandchildren's lives. This baby news was such a sweet surprise. Joe is a photographer and has stunning life-size photos of his grandchildren displayed in his home," the source shares. "Ashlee is so excited for Jessica because she knows how much her sister wanted this baby. Jessica and Ashlee are very close and often support each other when it comes to their kids."
A second source confirms to ET that "Maxi and Ace are so excited to have a little sister on the way. They talk about it constantly. They are telling everyone who will listen that they will have a new sibling."
According to the source, Simpson is "feeling great" amid her busy schedule. The fashion mogul is headed back home to L.A. after a recent trip to New York, where she had meetings about the Jessica Simpson Collection. The brand has color cosmetics and a new fragrance launching this fall. As for Simpson's music career, the source reveals that the song she performed with Willie Nelson at the Orange County Fair last month was one of her new tracks, and reveals that she's continuing to work on new music.
See more on Simpson in the video below.
Reporting by Adriane Schwartz.