The black and white pictures had "3 Months" written on it and showed the 33-year-old blonde beauty holding Ace close, with the tot looking straight at the camera, reported Us magazine.
The mother of two recently revealed her slim post-baby body just two months after giving birth when she stepped out for lunch.
Simpson also officially signed back on with Weight Watchers in August. She had reportedly earned USD 4 million in May 2012 in her first deal with the weight loss company while pregnant with Maxwell.