"Nighty Nite," she said.
The 34-year-old pop star and fashion mogul has shared photos of the kiddos before. She and Johnson, a 34-year-old retired NFL player, wed this past July. The two got engaged in 2010.
Their wedding was held at the lavish San Ysidro Ranch in Montecito, California and was attended by several celebrities. Maxwell served as a flower girl, while Ace was a ring bearer.
Jessica's sister, Ashlee Simpson, is also preparing to wed soon. She is engaged to Evan Ross, Diana Ross' son. Jessica recently attended her bridal shower, sporting a swimsuit and a gorgeous flower crown.