Once upon a time in children's theater, it was standard practice to entertain the little ones using wobbly stages with papier-mache puppets, treacly tales of frogs and princes, and actors whose beards came unglued before intermission.

But that was long ago. And to see how far children's theater has come, you have only to feast your eyes on the $9 million Family Theater that the Kennedy Center is opening today -- the first self-contained new theater to be christened at the center in 26 years. Built with federal funds in a space that formerly housed the AFI Theater, the playhouse is a significant facet of the center's five-year, $125 million effort to upgrade arts education.

The performance space, with plush seating for 324, contoured cherry-wood walls and a computerized system for maneuvering scenery, looks as if it could be home to Ibsen or Chekhov. The characters who will fill the stage, however, are far more likely to have been inspired by Maurice Sendak than Tennessee Williams. Located just inside the front entrance of the Hall of States, the new theater moves the family shows out of the center's attic and onto its front porch.

It makes a statement, too, about the escalating ambition of children's theater in the nation's capital and across the country, an increasingly diversified and grade-level-specific genre that is exploring ways to usher 6- and 16-year-olds alike into the world of live drama. In Washington alone, such institutions as the Kennedy Center and Bethesda's Imagination Stage spend a combined $25 million to $30 million annually on children's theater and the arts and education programs that support it.

And with its theater offerings, nationally touring shows and arts initiatives for students and teachers, the Kennedy Center's family-oriented projects reach about 11 million people each year, said Darrell M. Ayers, the center's vice president for education.

The Family Theater's initial offering, "Alice," a world-premiere adaptation of a children's book by Whoopi Goldberg that begins previews tonight, illustrates the artistic scale of the Family Theater's dreams. The $300,000 it cost to produce "Alice" (for which admission is $15) would settle the tab for an entire season at many small theater companies.

"When I arrived, I felt we were trying to fit family programs into our theaters whenever there was time," said Michael M. Kaiser, the center's president since 2001. "My feeling was that we shouldn't have to fit them into other theaters. They should have a theater of their own."

And that impulse carries a symbolic weight felt beyond the Potomac. The Family Theater is "hugely important," said Peter C. Brosius, artistic director of the Children's Theatre Company of Minneapolis, which in 2003 received the first regional theater Tony Award ever given to a youth-oriented troupe -- a citation that gave a psychological boost to the entire industry. "It's a validation of all the good work they've been doing, and it's also an announcement that this is a priority."

As the Family Theater suggests, children's theater is forging a more dynamic identity. Part of that has to do with a new generation of parents demanding more entertainment choices for their children.

"Nationally, there is a new level of sophistication in what's being done for kids," said Janet Stanford, artistic director of Imagination Stage, a nonprofit theater that produces six major shows a year on a $4.4 million budget. While the mainstream Broadway theater has long sought to open doors to the littlest playgoers -- the quest reached a commercial milestone in the mid-1950s, with Mary Martin in "Peter Pan" -- a growing number of cities, including Minneapolis, Seattle, Honolulu and Dallas, have developed highly regarded nonprofit children's playhouses.

The need for this kind of programming, Kaiser said, also arises because of the racier content of what passes for family entertainment at such places as Broadway: "When I was young, it was 'The Sound of Music,' " he said. "Now, it's 'Rent.' "

Not far from the Kennedy Center is the sleek, $12 million headquarters in Bethesda that Imagination Stage moved into in 2003 -- a complex funded by state and county grants and corporate and private donations.

Imagination Stage fills seats with elementary school-age students for plays it commissions, as well as those that originated elsewhere. Its current offering, "Seussical," is a version of a Broadway show, based on the classic books by Dr. Seuss, that was pared down for younger audiences by creators Lynn Ahrens and Stephen Flaherty.

"Seussical" -- a flop on Broadway -- has gotten a second wind in its new incarnation. In a testament to kid power, the musical is one of the most frequently mounted on the nation's regional-theater circuit. Imagination Stage's sweet production, with an affecting performance by Rob McQuay as the guileless elephant Horton, affirms the rightful serving of "Seussical" in a child's portion.

All that investment and adventurousness signals an understanding that theater for children is building ever more confidently on its franchise. It is in the children's category, in fact, that the Kennedy Center does most of its original work. Not only does the center's education department produce its own plays -- over the past 30 years, it has overseen 90 commissions, most of them for theater -- but it also regularly sends plays on tour across the country. ("Roald Dahl's Willy Wonka" opens tomorrow in Joliet, Ill., and "Alexander Who's Not Not Not Not Not Not Going to Move" just played Boise.)

Imagination Stage adapts and develops new work, too, putting on two original plays among six it presents each year. The profiles of artists willing to work in the form, from choreographer Debbie Allen to Pulitzer Prize-winning playwright Nilo Cruz, continues to rise. And Brosius said he is visited nearly every month by officials of one children's company or another who seek advice on building a space.

"Probably the greatest boom in theater construction is in our field," Brosius said. In October, his company celebrated the opening of a $27 million addition, designed by renowned architect Michael Graves.

In an indication of growing pains, the genre is undergoing something of an identity crisis. What, after all, constitutes children's theater? The label could be applied to anything from a preschool "Velveteen Rabbit" to a multimillion-dollar "The Lion King." At the same time, many companies are looking for ways to tap into an age bracket that they say has long been underserved: teenagers. The difficulty in bringing them into a theatrical fold that includes their younger brethren is obvious: Whenever older youngsters get a whiff of kiddie stuff, they're liable to be turned off.

Next month, the Kennedy Center has a hip-hop-inflected show, "Brave No World." Last February, Imagination Stage tried to snare older kids with a sci-fi show called "Calisto 5." And Brosius's company has in its repertory "Prom," a show with music that he describes as a kind of postmodern Bruegel painting.

"Even the phrase 'children's theater,' we don't like to use it because it sounds a little unsophisticated," said Kim Peter Kovac, the Kennedy Center's director of youth and family programming. The preferred nomenclature? "Theater for a young audience."

It's clear that in some way, every theater wants to be a theater for a young audience. So the competition for these impressionable playgoers -- and the parents who are looking for ways to entertain them, especially at holiday time -- is intense. Consider the options in Washington at the moment: "A Christmas Carol" at Ford's Theatre; "Damn Yankees," opening next week at Arena Stage; a cartoonlike "A Comedy of Errors" at Shakespeare Theatre Company. That's not to mention the touring version of the Broadway blockbuster "Wicked," which will arrive in the Kennedy Center's Opera House four days before Christmas.

Round House Theatre -- which began the season in September with an extremely adult "Camille" that included a graphic sex act -- is packing in the kiddies with "A Year With Frog and Toad," a children's musical that originated at Brosius's theater in the Twin Cities and had a brief Broadway run. The production is so popular that Round House has extended it for six performances -- four of them child-friendly matinees.

"There are lots of young families in this area, and we want to give them a theater experience they can share with their children," said Blake Robison, Round House's producing artistic director. The older folks who are the core of the Round House audience are bringing their grandchildren, he said, and business is running 40 percent ahead of projections. "It broadens our audience for the future," he said, "and yes, financially, it helps us pay for the more challenging fare."

Even the estimable Shakespeare Theatre Company seeks to seduce tweeners with 400-year-old "thees" and "thous." In March, it tested an hour-long "As You Like It" at the Kennedy Center. Although the experiment, aimed at middle schoolers, yielded middling results, the company said it wants to develop more family fare for the program expansion that will come with a new main stage, which is being built downtown.

Between the Kennedy Center's Family Theater and the two impressive spaces at Imagination Stage, the physical surroundings for young people's theater in Washington have never been more welcoming. (Other, smaller companies, such as Classika-Synetic Theatre, also produce theater for children.) The classic challenge, of course, is how to fill those spaces effectively. Stanford, artistic director at Imagination Stage -- founded in 1979 and for many years housed in a storefront in White Flint Mall in North Bethesda -- said her company began commissioning plays partly because "there were no good scripts" and she wanted the plays to be entertaining and brimming with meaning.

" 'Serious intent' are my watchwords, even if the material is not heavy," she said. "This is a place to prepare your children for life, not to protect them from it."

Each year, the library of producible material expands a bit, thanks to such playwrights as Kim Hines, who was asked to adapt Goldberg's "Alice" -- which recounts the adventures of a money-crazed little girl obsessed with a lottery ticket -- for the Kennedy Center. A former child actor who lives in Minneapolis, Hines said there's still a bit of a stigma attached to writing for children, as if it were "not really writing a play." When other writers offer such observations, she said that her reply is: " 'I challenge you to write a piece for a younger audience. It's not easy. There are all sorts of boundaries, limitations, less time to make your point.' "

It's the sort of challenge that appeals to her. Another challenge she likes is making the play inviting for adults, as well. "At the Kennedy Center, they called and asked me, 'Can you write "Alice" for the middle-school age?' I said, 'Yeah, but I'm going to write it for all ages, because parents have to sit through this, too.' "

In that vein, Imagination Stage also has a generous heart. As the lights dim for "Seussical" in a theater filled with 5-year-olds on a recent Saturday afternoon, a voice on the loudspeaker makes an announcement. It comes as even more welcome than the arrival of a fairy godmother: "Parents, please be sure that all children remain seated during the performance. There is a quiet room in the far right corner of the theater. This is a good place to take any restless children."

For noisy kids, Imagination Stage has installed a soundproof booth. Few innovations say "grown-up-friendly theater" better than that.

Audra Alise Polk with Nehal Joshi, left, and Scott Kerns during a dress rehearsal for "Alice," which will open the Kennedy Center's new $9 million Family Theater today.

Audra Alise Polk is the title character in "Alice," which is making its world premiere in a Kennedy Center venue that -- along with Bethesda's Imagination Stage -- reflects the escalating ambition of children's theater across the country.