"Our girls are working on names. At first they were definitely Disney. It was like, Donald Duck, Minnie Mouse Affleck," Garner, 39, said on "The Tonight Show" on Wednesday. "And then they've moved on. Then it was Peter Pan, Captain Hook, Smee."
"They're coming up with lists and coming in and saying, 'Let's have a baby-naming contest! Let's have a baby-naming poll!'" the "Butter" star added. "They ask everyone, because they just want to know. But we're not telling."
Garner said she knows the sex of her baby, though she chose not to reveal it on "The Tonight Show." The actress previously said she's hoping for a little girl, but she isn't sure if Affleck, 39, feels the same way.
"I would have thought [he wanted a boy]. At first I think I really thought so," Garner told host Jay Leno. "And then he kind of said, 'Well, we have girls. We know how to do girls. My girls love me. I'm the big guy in the house.' So, now I'm not sure."
Garner, who announced her third pregnancy in August, is due in late February/early March.