Emma has uploaded a couple of intimate snaps of three-week-old Evelyn Penn Willis to the social media site.
In one of the photos Evelyn gazes in wonder at her older sister, two-year-old Mabel, who is gently cradling her head.
Emma captioned the image of the two sisters: 'The start of a beautiful friendship.'
Little Evelyn will have plenty of sisterly support, as 59-year-old Bruce has a total of five daughters, including three with his ex-wife Demi Moore.
Thanks to a rather large age gap between the siblings, we reckon Rumer, 25, Scout, 22, and Tallulah, 19, are going to be regularly called on for babysitting duties.
The other photo Emma uploaded was taken by Bruce himself and shows 35-year-old Emma breastfeeding Evelyn.
Emma captioned this image 'Breakfast of Champions. Photo credit: B. Willis.'
While he is more than happy being surrounded by women, Bruce is keen to add a son to his brood. "Eventually, I'd like a son. But I'm okay now," he recently told People magazine.
Speaking of Evelyn's arrival the star said: "[We] didn't know what we were gonna have until the baby came out.
"In general, I think women should be in charge of everything. They should be running the country.
"Even if I had five boys, I'd still feel the same way."