And Broadway has acquired a vital youth audience. Walk past the stage door of the St. James Theater after a performance of “American Idiot,” the new musical based on the Green Day album of the same name, and you’ll see teenagers crowding the barricades like bobby-soxers in the early heyday of Frank Sinatra. It’s the same deal with the current revival of “Hair” at the Al Hirschfeld Theater, which will close in two weeks after a surprisingly robust run of more than 500 performances.

“We knew people of my generation would go for it  I’m in my 50s,” said Oskar Eustis, the artistic director of the Public Theater, under whose auspices the revival originated in 2008 at the Delacorte Theater in Central Park. “But I was shocked at how it immediately became this thing with young people. There are dedicated youngsters who come back multiple times. They’re always the first ones who come up on stage at the end. They actually call themselves ‘Hairballs.’ ” Last winter, Mr. Eustis and his fellow producers shrewdly took advantage of the big snowstorm of Feb. 10, which closed schools citywide, by offering steeply discounted Snow Day tickets to anyone with a student ID.

The Broadway babies are not the passive, bused-in tourist young people of yore who went to see “The Phantom of the Opera” or “A Chorus Line” simply because it was what one did when visiting New York. They’re true believers for whom love of musicals brings happiness, transcendence, and, strangely enough, social acceptance.

Ask Fred Hechinger, a fourth grader at the Manhattan School for Children, which shows he has seen in the last year or so, and his response sounds like the A-B-C listings in The New York Times’s arts section: “ ‘Gypsy,’ ‘South Pacific,’ ‘Finian’s Rainbow,’ ‘A Little Night Music,’ ‘Hair’ three times. A lot of Off-Broadway stuff, too.” Fred’s theatergoing habit has the support of his parents, Paul and Sarah, and, more notably, his classmates. “When I was 5, 6, 7, there weren’t as many kids seeing shows, but now most of them do,” he said. “There are maybe, like, three kids in my school who don’t like theater.”

My daughter, 14, is also a member of the genus Showpeople. She has seen “Hair” four times. She spends summers at a theater-arts sleepaway camp in the Catskills called Stagedoor Manor. She not only watches “Glee” raptly, but also is sufficiently fluent in musical theater to have remarked, when the actor Jonathan Groff materialized in an April episode as a new romantic interest for Rachel, “It’s a ‘Spring Awakening’ reunion!” (Mr. Groff and Ms. Michele starred in that Tony-winning Broadway show, which seems in retrospect as significant a cultural portent as “High School Musical.”)