WASHINGTON - The grand ballroom at the Capital Hilton glowed neon purple, and Idol-er David Archuleta's "Crush" pulsed from giant speakers.

Less than a mile from the White House, the First National Tween Girl Summit - yes, summit - was under way. The event was part serious confab, part sparkly hearts and butterflies - just like its audience.

That would be those conflicted wannabe teens (but not quite there yet) - the 8- to 12-year-olds known as tweens.

On this recent Saturday, 250 girls came from across the country, including the Philadelphia region, to speak out on issues that mattered most to them. Sure, pink outfits and blue fingernail polish ruled. But the day was dedicated to issues heavier than a loaded Hannah Montana backpack - what tweens had to say about body image, bullies, unorthodox careers, and more. All the while, adults with long titles listened and took notes.

"We got the power," 10-year-old Sierra Arnold of Charlotte, N.C., belted at day's end.

The tune well could be the anthem for Arnold and her preteen friends.

By all estimates, the current crop of tweens, 20 million of them, are the it generation. They can't drive to the mall, but they are mighty consumers (even in the recession), believed to control or influence as much as $200 billion in purchasing power. And those numbers are expected only to grow. By 2015, the census estimates that tweens will number nearly 24 million.

Youth have always influenced pop culture. But today's tweens, maturing faster emotionally and physically than previous generations, show a sophistication (about technology, clothes, you name it) not usually seen until the teen and young adult years, marketers say.

"These so-called prepubescent children have given way to a much cooler, trendier, savvier tween," said Josh Weil, a founder of the New York-based marketing firm Youth Trends. "A lot more is expected of them, academically, athletically, and socially."

As Caitlin McDermott, 9, of Washington said: "We tweens have something to say. We're not just little kids."

Two of the most famous in-betweens live at 1600 Pennsylvania Ave. The Obama girls, 8-year-old Sasha and 11-year-old Malia, are known in some circles as the First Tweens, as they set trends (remember how everyone wanted their J. Crew coats?), exude poise, and care about the larger world.

Companies are cashing in on this tween influence, eager to seal brand loyalty at ever younger ages, said Scott Testa, a professor of business at Cabrini College who specializes in the demographic. More than ever, the marketplace is pushing a tween lifestyle heavy on teen aspiration, despite concerns from developmental experts - and even marketers themselves - over the loss of childhood.

Lyn Mikel Brown, a professor of education at Colby College who cowrote the 2006 Packaging Girlhood and the just-out Packaging Boyhood, said the very notion of tween - a marketing term, not a developmental stage, she notes - is "an erosion of any kind of boundary between childhood and adolescent. It's marketing a very stereotypical, teen life."

Consider the latest additions to the tween world:

This month, AOL launched its new blog, JSYK (just so you know in text-speak), with fashion, celebrity, and "real life" news. Its booth at the summit was mobbed.

In the spring, the creators of Bratz introduced Moxie Girlz. More conservatively dressed than their oft-criticized cousins, the dolls aimed squarely at tweens come in different "personalities" and tie in to an online Best Friends Club. "It's about girls who are confident," said exhibitor Jason Larian, head of marketing for MGA Entertainment. "You can be whoever you want to be. You have moxie."

Social networking Web sites for tweens have exploded from a handful a decade ago to hundreds. And thank tweens for the mega-brands known as Miley Cyrus, the Jonas Brothers, and Twilight. (If the tween appeal seems heavy on girls, it is. Marketers say they have found boys harder to reach.)

The environment was ripe for a tween girl summit, that last word chosen intentionally for the import it carries, organizers said.

"They impact so much of what goes on in our world," said Denise Restauri, founder of AllyKatzz.com. The social networking Web site for tweens with 75,000 unique visitors a month hosted the girl gathering.

"It's never small change that these girls influence. But it's beyond economics," said the market researcher, who also heads AK Tweens, which extracts trends from the tween chatter on its Web site. "They deserve a platform. They're a generation that wants to fix the world."

The summit tweens, which included girls as old as 14, spoke out about the environment, world peace, and children's rights.

"Save the walruses," said one girl as her message to the world.

"Girls rock no matter what," said another.

And "I love chocolate." They are kids, after all.

"The world, we need peace, trust each other, believe in everyone, help when you get a chance," Nikki Adeli, 12, of Center City wrote on a card that was posted with everyone else's on the "White House Wall," which was to be presented to President Obama or, more likely, his staff.

The seventh grader is typical of the tween model marketers pursue. She blogs on AllyKatzz, cares about world peace and healthy habits, and admires celebrities but realizes that pictures are often airbrushed to perfection and that not everything they say is true (which is why brand strategists are constantly rethinking ways to reach tweens).

"I thought it would really be cool to learn about girls' lives," she said of the summit. "I wanted to become a better leader."

A lot of girls, she said, might doubt themselves, though she didn't seem to be one. "They see the presidents of the United States, and they're all men," she said. "But just because you're a woman does not mean you can't do anything. You can do tons."

At Greenfield Elementary School, Adeli helps lead a walking club. She also talks up the benefits of drinking milk with classmates as an ambassador for the National Dairy Council, which sent her to the summit.

"What would you rather have? Strong bones or osteoporosis?" she said during a discussion of eating habits and childhood obesity.

Amy Jagodnik, who lives in D.C., said she brought her twin daughters Caitlin and Camille with some reservations.

"Is this a marketing ploy or is this really something more important that's going to empower them to do something more than watch the Disney Channel?" she wondered.

The answer was probably a little of both. Amid the messages of grrrl empowerment was an exhibition hall that hawked products - the Dream Phone Game, Charm Girls Club (an online game where girls can "attend the ultimate prom, create your own amazing fashions, take your mall from drab to fab, and party with your friends!"), and Flipoutz accessories (yet another interactive, collectible item).

Soccer star Brandi Chastain was there. And three Redskins cheerleaders. So was self-esteem expert and Seventeen columnist Jess Weiner and a fatigues-clad Col. Catherine Ellen Abbott, chief of the media relations division of the Army.

A panel of executives in the fields of international policy, health care, sports, academia, and marketing listened to the girls respond to prompts about what worries them (peer pressure, war, bullies, the size of their bodies, their hair, their grades), how they are judged by others (too often by outward appearance rather than what's inside, and boys always underestimate them), and what they think of the media (too many celebrity-focused stories rather than stories about real girls).

Erin Moran, 13, of Sewell, came with friend Brianna Britton, also 13, of Mantua.

They came mainly to hear the new pop sensation boy band WOW that was playing that evening at the summit, they said. But they also liked the opportunity to talk about issues important to them.

One of the big ones was the conflict between what they want and what others want for them.

"My sister wants me to play lacrosse," said Britton. "I want to be a singer."

"I'd like to think I'm in control of my life," Moran said, "but my parents are. They have dreams for me. . . . I want to live my own life." Her parents, she said, want her to be a teacher or lawyer, but she likes music and writing.

The summit concluded with pledges. Sierra Arnold promised to help girls in other countries who have less than she does and to stand up to bullies.

At the same time, the tween said: "I'm a kid. I have a lot of years to go. I don't know if I should worry about this stuff. My biggest worry is puberty."