NY DAILY NEWS – As off-screen do-gooders go, Captain America takes the cake.

Actor Chris Evans, star of “Captain America: Civil War,” surprised a packed Manhattan movie theater full of young volunteers Wednesday night for a special New York Daily News/Disney charity screening of his new movie.

And he even led the audience in serenading a soon-to-be-13-year-old good Samaritan with a rousing “Happy Birthday” — while toting a superhero-themed cupcake and Captain America toys for every kid in the theater, courtesy of the movie studio.

“Knowing that the role, though demanding and though heavy with responsibility, you get that type of reaction and it’s all worth it,” Evans told the Daily News immediately after exiting the theater.

It reminded him of the time he met his idol, Hulk Hogan, and got an action figure signed as a child.

“I feel like I am those kids screaming,” he said. “Because I remember what it was like when I was a kid. When things really drove me wild.”

The screening honored a pair of charities that encourage kids to volunteer. GenerationOn, the youth services division of Points of Light, inspires, equips and mobilizes kids to improve the world through volunteer services in their communities.

“It’s really great to see someone of his standing interested in this stuff, because it makes people see what needs to be done. … Wow, Captain America believes in this? We should too,” said Eden Duncan-Smith, a 16-year-old volunteer with Generation On.

CelebrateU, founded by a pair of teens, organizes birthday parties for less-fortunate kids in shelters.

“We were really excited to come to the movie in the first place, and we had no idea he was going to be there,” said Chase Cauder, 16, cofounder of CelebrateU. “And when he came out we were like wow.”

On Wednesday, the tables were turned on one of that organization’s volunteers. Archie Silverstein, who turns 13 this month, was himself feted. He had recently donated his Bar Mitzvah gift money to the charity.

“It was pretty awesome to see a guy I admire so much come out of nowhere and wish me a happy birthday. It was so insane. I had no idea,” said Silverstein.

In “Captain America: Civil War,” opening late Thursday, Evans reprises his role as the star-spangled hero, facing off against his most dangerous foe — his old Avengers teammate Iron Man (Robert Downey Jr.) — over a push to bring superheroes under the government’s control.

But before the lights dimmed, Evans put the spotlight on the assembled kids, thanking them for helping to make the world a better place without CGI superpowers or stunt doubles.

“It’s a cool thing to think you might have a place in one of their chapters of their childhood,” said Evans.