"It seems like every time we ask her, it's a different farm animal," Garner told PEOPLE recently. "My oldest daughter [Violet, 4] has a very clear idea, but it's contingent upon my younger daughter."
She adds: "Costumes are not ready in my house. Now, I'm realizing I need to at least get the orders in."
Garner, who earlier this month launched a campaign with Frigidaire to support Save the Children's work for kids in need, is also already prepared to counter any potential sugar rush.
"I'll make up some rules," she says.
Juggling family life, work and philanthropy, Garner says she's doing her best to strike a balance. "No matter what, it is very tricky and difficult – just to be a good parent at all," says Garner, who had been filming Arthur with Russell Brand and Helen Mirren. "I have a lot of help. And for that I'm very grateful.
As for looking put-together, she recognizes one great perk. "I wish every mom could have a hair and makeup team once a week to show up and fix them up," she says.