And, of course, the delighted grandparents were right there with her and husband Marc Mezvinsky as they left the hospital.
"Marc & I are very grateful to the drs, nurses & staff @lenoxhill for their excellent care," she Tweeted shortly after 7 p.m. Monday.
Well-wishers on the New York sidewalks yelled "Congratulations" and "Mazel Tov" to the family, who were all smiles.
"Charlotte will be welcomed by a lot of cousins," her paternal grandmother, former Pennsylvania Congresswoman Marjorie Margolies, tells PEOPLE.
With 10 aunts and uncles on her father's side, Charlotte has 18 first cousins (so far) on the Mezvinsky family tree. "They are thrilled."
Charlotte Clinton Mezvinsky was born at 7:03 p.m. on Friday, Sept. 26.