Girls rule. In the world of entertainment, they're royalty, princesses at the cash register. And when they like something, they really, really like it, watching and listening and buying again and again.

The power of tweens' wallets and their parents' credit cards is so significant as to influence CD and DVD sales, television viewing, Broadway and concerts.

Skyrocketing ticket prices for the Miley Cyrus/Hannah Montana "Best of Both Worlds" concert in "secondary markets," long known as scalpers, are inviting probes by state attorneys general and commentary by Federal Reserve economists. Kerry Inman of Pennsville, N.J, filed a lawsuit last month in federal court after failing to secure Atlantic City seats through the Miley Cyrus fan site.

Tickets for tomorrow's sold-out appearance at Philadelphia's Wachovia Center are being offered for $225 (for poor seats) to $2,500 through Web vendors, more than 35 times the official price and higher markups than for seats at recent Bruce Springsteen and Sting concerts.

Parking vouchers are being scalped for $25.

In an unprecedented move, the Wachovia Center will open its doors from 1 to 6 p.m. today so fans can purchase Hannah/Miley and Jonas Brothers (Kevin! Joe! Nick!) merchandise in time for the holidays, no tickets required, beat the concert crowd, all major credit cards accepted.

There are an estimated 25 million American tweens, those between ages 8 to 14, with an annual spending power of $180 billion, according to Alloy Media & Marketing - thanks, in large part, to their generous baby boom parents.

A large difference today is that producers recognize the "co-purchasing dynamic" of "Millennial" tween girls shopping with parents' approval and appropriated dollars, Alloy executive vice president Samantha Skey said. "Shows are not only showcasing characters that are close to their parents, but creating properties that parents can tolerate. The big difference between the Millennials and Generation X, which was a smaller demographic and a little more misanthropic, is that they're close to their parents."

While boys generally leapfrog from children's entertainment to action fare, teen games, Internet sites and music, tween girls - the phrase is almost redundant - command their own sizable sweet spot of entertainment and its associated merch.

Nowhere is that more realized than in the demand for all things Hannah.

"I'm so excited to be going," said Carly Shapiro, 11, of Bala Cynwyd, who will attend the concert with her 12-year-old cousin, Hannah Ceisler. "Hannah Montana makes me laugh. I like that she gets along really well with her family." And she plans to pick up a T-shirt, too.

Miley Cyrus and Hannah Montana - who, for the uniformed, are one and almost the same, a winsome 15-year-old singer-actress and her blond rock-star alter ego - helped Disney prevail in 2007 record sales.

In the era of downloads and a battered recording industry, tween girls are the rare fans still purchasing compact discs.

Two of the year's top-10-selling CDs were bought largely by tween girls:

Hannah Montana 2: Meet Miley Cyrus

(No. 4) and

High School Musical 2

(No. 8),

which hit No. 1 on the Billboard 200

. Each sold more than two million units.

"All of a sudden, I'm in the music business," said Gary Marsh, entertainment president of the Disney Channel Worldwide, which reaches 90 million American homes. "Radio no longer sells music. Television does."

And girls are the market. "The reality is that we hold on to the girl audience much longer than boys," Marsh said. Almost two-thirds of Disney's older viewers, ages 9 to 14, are female.

High School Musical 2

, like its 2006 predecessor, is the juggernaut. The Aug. 17 Disney Channel debut attracted the second-highest audience in cable history, 17.2 million viewers, bested only by ESPN's

Monday Night Football

matchup Dec. 3 between the New England Patriots and Baltimore Ravens with 17.5 million.

The movie industry generally caters to male audiences with action, science-fiction and comic-book fare, which are easier to market globally. But television is delighted to step in, with the Disney Channel leading the way.

High School Musical 3

, a feature film, is in the works for next year, as well as a

Hannah Montana

feature film, the cable

Cheetah Girls 3

in India (a big Disney market), and a Jan. 11 cable movie called

Camp Rock

, starring the Jonas Brothers and Demi Lovato, whom Marsh is grooming as the next Miley.

All of these projects will arrive with more CDs and a flood of other products.

Fear not: If a girl misses tomorrow's Hannah/Miley show, Disney is producing a 3-D concert film for release early next year.

"Girls are the original consumers, and the last of the shoppers," said Stephanie Savage, co-executive producer of the CW's hit

Gossip Girl

, renewed after three episodes due to impressive DVR use.

While boys are drawn to home and Internet entertainment, shopping remains a novel and highly social experience for girls, one with serious ramifications in entertainment. Shows extend into music and DVD sales, ring tones, Web-site traffic, and clothing.

Times Square has become a theatrical mall, a magnet for girls and their parents. Six of Broadway's top-10-grossing shows are family entertainment.

Legally Blonde

and

Wicked

feature strong, intelligent female leads in Elle Woods and Elphaba. A quarter of

Wicked

's demographic are younger than 20, considerable given that few girls attend school-night performances. And those girls do love to buy the $125 "swElle Swag" combo complete with 6-foot pink boa or the four - count 'em, four -

Wicked

apparel collections.

Carly Shapiro, a sixth grader, has already seen

Wicked

,

Mamma Mia

and

Hairspray

, with tickets for

Blonde

in January. In development for Broadway are

Princesses

,

Wanda's World

,

The Little Mermaid, Thirteen

, and a musical version of

Clueless

.

Despite weak reviews,

Grease

performs at 95 percent capacity, garnering young crowds (with their nostalgic parents) thanks to the NBC talent search

Grease: You're the One That I Want

this year. The stage production of

Legally Blonde

aired six times on MTV this fall, helping propel the soundtrack to near the top of the charts.

"When kids respond to something on TV, they want to see it again and again,"

Blonde

producer Hal Luftig said.

Aspirational entertainment, the story of a girl slightly older than the targeted audience, is ideal for tweens.

"When I saw the movie, I thought this was the perfect story for young girls, a strong heroine who thinks she wants one thing and makes a journey to find out that it's OK to be smart," Luftig said. Following in the footsteps of

Wicked

's wickedly successful tour,

Blonde

will embark on a two-year national tour next fall, naturally with a full and active lobby boutique.

"If you don't market a teen drama to the core group of younger girls, you're in trouble," said

Gossip Girl

's Savage, who was co-executive producer with Josh Schwartz of the hugely successful

The O.C.

on Fox. "They want the thing that's slightly out of their grasp, that's not completely age-appropriate."

Though

The O.C.

and

Gossip Girl

focus on the wealthy, albeit on opposite coasts, the real hook is that the dramas manage to show cool parents interacting with cooler children, attracting tweens and their parents.

That's huge in tween entertainment, and inspired marketing. When parents approve, they're more willing to open their wallets. In today's shows, parents aren't buffoons or absent. They're very much present and involved.

"Parents are the most important people in [kids'] lives. We've done marketing. They're their heroes," Marsh said. "When we hit the market, the bell rings very loudly."

Nickelodeon is chasing those same dollars, with a Naked Brothers CD, a multiyear relationship with Sony Music, and a brand extension with T-shirts at Lucky Brand Jeans. It has movies in the works, including

Angus, Thongs and Full-Frontal Snogging

, which Pamela Kaufman, Nick's executive vice president of marketing and worldwide promotions, likened to "

Bridget Jones's Diary

for the 14-year-old."

"The new normal is the digital family, the entire family dynamic together with parents pressed for time," Kaufman said, "involving their kids in all kinds of decisions, music, fashion and travel."

Toward that end, Nickelodeon will open a theme park next year in Minnesota's Mall of America. The company plans free-standing themed resort hotels including water parks, interactive entertainment, spas, family suites and "retail offerings," 20 locations planned for all over the globe with the catchy name Nickelodeon Resorts by Marriott.

Better book now. Beat the crowd.

Contact staff writer Karen Heller at 215-854-2586 or kheller@phillynews.com.