How the 'Loving' Julie Andrews Was Like a 'Nanny' to Her Young Sound of Music Costars (Exclusive)

Julie Andrews was just as doting in real life on the set of The Sound of Music as her governess character Maria, according to her young costars.

Now all grown up 60 years after the classic musical debuted in theaters, Duane Chase — who played younger brother Kurt von Trapp — tells PEOPLE that Andrews, 89, "was kind of a nanny for" the younger children on set.

"[Charmian Carr, who played oldest von Trapp child Liesl], of course, was older, but for the rest of us being 13 or 14 on down, she helped, I wouldn’t say, keep us in line but corralled us," he says.

While not filming, Andrews was also "super nice" and engaged with Chase and his young costars: the late Carr and Heather Menzies (Louisa von Trapp), plus Nicholas Hammond (Friedrich von Trapp), Angela Cartwright (Brigitta von Trapp), Debbie Turner (Marta von Trapp) and Kym Karath (Gretl von Trapp).

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"Oftentimes we'd have breaks in filming, and so we'd all be sitting around on a huge blanket. And we'd be playing cards [with Julie]," he says.

Andrews' daughter Emma, who "was a baby at the time" of filming, "would be on the blanket with us too," Chase continues, adding, "It would be really fun to see Emma again after all these years."

Before she went on to win a Best Actress Oscar for Mary Poppins — a category she was also nominated in the following year for her role in The Sound of Music — Andrews treated the kids on the Music set to what would become a classic tune in cinematic history.

"She taught us 'Supercalifragilisticexpialidocious,' " Karath tells PEOPLE, sharing that Andrews even played it on the guitar. "So we were privy to hearing that song before Mary Poppins even came out."

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What Chase "remember(s) most" about working with Andrews on the film was having "all [the child actors] and our mom and dads and other people who worked behind the camera over to her house for an all-day pool party."

"I thought that was just really incredibly nice on her part," he tells PEOPLE.

Karath remembers having "very fun times" with Andrews "behind the scenes or while we were waiting" for a scene to be set up.

"She was really warm, and congenial, and loving, and patient, and very, very sweet," she adds. "That's who she is — she's wonderful. She's a really wonderful person."

For more from Chase and Karath surrounding The Sound of Music's 60th anniversary, pick up the latest issue of PEOPLE, on newsstands now.