Robert Pattinson and Kristen Stewart on November 14, 2011 in Los Angeles, California. Credit: Steve Granitz/WireImage

Life imitating art!

Kristen Stewart and Robert Pattinson were bitten by the baby bug while playing parents in November 16's The Twilight Saga: Breaking Dawn - Part 2. On set, Stewart, 22, and Pattinson, 26, connected with 11-year-old Mackenzie Foy, who plays their half-vampire, half-human daughter, Renesmee.

In rare unguarded moments for the fiercely private couple, they let themselves imagine life as parents. "They would talk about how they would raise their own children," a set source tells Us Weekly. "Kristen would say, 'Well, I'd never do this or that.' Sometimes it would start off as a joke, but you knew they were really thinking about it."

And, when the couple -- who has been together for three years -- attended a friend's wedding on June 23, they seemed more interested in what comes after marriage: the baby carriage.

"Kristen was talking to a pregnant guest and told her that she would love to have a baby with Rob," says the source. "She thought it was so cool -- at one point she touched the woman's belly to feel the baby kick."

Pattinson, for his part, has long known that Stewart is the mother of his future children.

"He is over-the-moon in love with Kristen," says a Twilight source. "For him, she's The One, so it's just a matter of when they decide to have kids."