Playing a loving wife and husband came easy for Jennifer Garner and Ed Helms.

During the production of their new Netflix holiday movie Family Switch — about parents who magically swap bodies with their two teens — the stars turned the set into a bonding experience.

“We didn’t disperse when somebody said, ‘Cut,’ ” Garner, 51, a mom in real life to Violet, 18, Seraphina, 14, and Samuel, 11, with ex-husband Ben Affleck, tells PEOPLE in this week’s issue. “We all stayed and hung out and played with the babies.” (Those would be twins Lincoln and Theodore Sykes, who appear as the couple’s youngest child.)

Jennifer Garner and Ed Helms in Family Switch.COLLEEN HAYES/NETFLIX

And if they could switch bodies with their own children? “I’d want to switch places with Ed’s kids,” says Garner. “I want to be that little one who has a crazy look in her eyes running around in a diaper. Break out the paint and the glitter and go ham on the house.”

Helms, 49, who doesn’t publicly disclose his wife or kids’ names, understands Garner’s impulse.

“Yeah, my kids are ridiculously cute and insane,” he says. “The first thing I would do is eat a ton of junk food because that’s what they can do. They’re these little furnaces. You can just put anything in there, and it churns up. So I would eat cookies, ice cream, cake, cupcakes—all of it. Pizza all day long.”

Jennifer Garner and Ed Helms.JENNIFER GARNER/INSTAGRAM

As for Garner, she playfully insists there’s no strong desire to revisit her past.

“You know what? I think my kids work so hard, and they have so much pressure on them that I could never even have imagined as a teenager myself,” she says. “I’ll stay right here in my old lady body, thank you very much.”

Family Switch starts streaming on Netflix on Dec. 30.