The 51-year-old actress adopted the 3-year-old child in early December, giving her son, Louis, 5, a younger sister.
"It's like he's been waiting for her," Bullock told Access Hollywood.
"Nothing has changed and everything has changed, but it's not different."
"I don't know how to explain that. It's like she's always been there, or we were always making room for her and waiting for her."
Bullock, who is dating photographer Bryan Randall, says there is noth much change but things have altered a bit.