Ryan Reynolds and Blake Lively Celebrate His Birthday with Family Visit to Broadway's & Juliet (Exclusive Details)

What do you get the guy who has everything? Apparently, tickets to a Broadway show!

Ryan Reynolds marked his 48th birthday on Wednesday, Oct. 23 with a matinee visit to the Tony-nominated musical & Juliet, alongside his wife Blake Lively and three of their four kids, daughters James, 9, Inez, 8, and Betty, 5.

The outing was Lively's idea, a source on the scene at the Stephen Sondheim Theatre in New York City tells PEOPLE.

"I don't know what to get him for his birthday? What do you get him for his birthday? I know he loves musicals, I love musicals, the kids love musicals. So it felt like the right choice!" she told the cast, according to the insider, when she and Reynolds visited with them backstage after the performance.

& Juliet imagines what would happen if the title heroine from William Shakespeare's classic romantic tragedy Romeo and Juliet would have survived and gotten a second chance at life and love on her own terms. The musical's book was written by David West Read, the Emmy-winning writer from Schitt's Creek. 

All of the action is set to a score of chart-topping pop songs from the catalogue of five-time Grammy-winning songwriter and producer Max Martin.

Those include songs made popular by Britney Spears ("Baby One More Time"), Kelly Clarkson ("Since U Been Gone"), Pink ("F---in' Perfect"), Justin Timberlake ("Can't Stop the Feeling"), Bon Jovi ("It's My Life"), Katy Perry ("Teenage Dream"), Demi Lovato ("Confident"), Céline Dion ("That's the Way It Is"), Backstreet Boys ("I Want It That Way"), *NSYNC ("It's Gonna Be Me"), Ariana Grande ("Problem") and many, many more.

Lively, the source says, told cast members she was aware the musical had "a lot of hit songs in it" but was "blown away" by "how really well-written it is."

The 37-year-old actress also joked about how much the kids liked the show, the insider shares. "She teased to them, 'The kids want to come tomorrow. They think they're coming back every day.' "

Reynolds and Lively also share 1½-year-old son Olin, though the toddler didn't attend the show. The family came to & Juliet quietly, and told the cast, per the insider, that they didn't initially intend to go backstage but thought the show "was so amazing they needed to come say hello."

Both showered the show's stars — including principals Ben Jackson Walker, Drew Gehling, Maya Boyd, Tiernan Tunnicliffe, Paulo Szot, Philippe Arroyo and Justin David Sullivan — with praise, posing for individual and group selfies.

"They were just raving about how good it was," says the source. Lively also snapped individual pictures of Reynolds on stage.

To no surprise, Reynolds' sarcastic sense of humor was on full display. "He immediately started joking with the cast," the source says, recalling how Reynolds told them, 'This is the best things I've ever seen in my life. You are all so talented, it's ridiculous. You guys are the ones in showbiz, I'm such a fake! I could never do what you all did.' "

"He was very, very sweet and generous with his time," a second source on the scene adds. "Blake too — couldn't have been kinder. They stayed a long time, and really made sure every actor felt seen and appreciated."

The & Juliet cast shared their appreciation right back, taking time to teach James, Inez and Betty some choreography from the show and dance it with them. The Broadway stars then all sang "Happy Birthday" to Reynolds, a sweet moment that Lively recorded on her phone.

"It was a great afternoon for the cast, many of whom made their Broadway debuts in this show," the second insider says. "To have their work praised by two of Hollywood's biggest stars is something they'll never forget."

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Reynolds and Lively celebrated their 12th wedding anniversary last month, a source telling PEOPLE at the time that “Blake and Ryan are a great team when it comes to both their family and work.”

“They're super supportive of each other. He's very proud of her,” the source added. “They have a great marriage and love to celebrate everything they created together.”

Both are coming off of huge summers at the box office, with the releases of Deadpool & Wolverine and It Ends With Us. His movie, in which she cameoed, made history as the highest-grossing rated-R movie of all time. It Ends With Us, meanwhile, became Lively’s highest grossing film, surpassing 2011's Green Lantern — which is where she and Reynolds first met.

Tickets for & Juliet are now on sale.