From PEOPLE Magazine Click to enlarge
Among the hundreds of kids who showed up to audition for a spot on Barney & Friends back in 1999, there were two 7-year-old brunettes, who happened to stand in line next to each other and who decided to plop down on the pavement and start coloring together. Since that moment, says Demi, Selena has been "my best friend in the entire world!"

But even before the two future tween queens, now both 16, met, they each had a colorful start to their careers. Growing up in Grand Prairie, Texas, Selena was only 6 when she caught the acting bug as she watched her mom, Mandy Teefey, perform in local theater productions. "She loved going to rehearsals with me," says Mandy, 33, who separated from Selena's dad, Ricardo, when Selena was 5 and married Brian Teefey in '06. "One night she started critiquing the actors. I thought, 'Oh boy here we go...' "

About 25 miles away in Colleyville, Demi got her early exposure to the stage by performing in pageants. "It taught Demi a lot about auditions," says her mom, Dianna De La Garza, 46, a former Dallas Cowboys cheerleader and country singer. "She was able to learn at a very young age how to express herself and carry herself in a room with judges." But when the final callback came for Barney, Demi had to choose between competing in an international pageant or staying home for another round of auditions. "We sat her down at an ice-cream store, and I said, 'Listen, you can either pursue Barney or go on this trip,' " says Dianna, who split from Demi's father when Demi was a baby and married Eddie De La Garza, a former car-dealership manager who now helps manage Demi's career. "She thought about it for two seconds and said, 'I want to stay.' "

Good choice: Not only did she land her first acting gig, she sealed her friendship with Selena. "When we started shooting, Selena was always my favorite," says Demi. Once Barney gave them the boot—"They said I was getting too old," says Selena—Selena filmed commercials and a small part on Spy Kids 3-D: Game Over, and Demi worked with a modeling agency and took piano and guitar lessons, but all the while they made time for regular hang-out sessions. In 2006, Hollywood called: Selena was cast in a new Disney Channel show called Wizards of Waverly Place and relocated to L.A. by early 2007. "There were tears, crying and everything," says Selena. "We both auditioned for Disney. She didn't get it. I did. We've had those moments, but we're so proud of each other that it doesn't affect us." In fact, it made their bond stronger. Demi, with her mom and two sisters Dallas and Madison, moved to L.A. with Selena and her mom so she could audition for other roles. Says Demi: "Selena always believed in me."

Demi's time came in June 2007. After appearing on Disney Channel's As the Bell Rings, she scored the leading-lady spot in Camp Rock, opposite the Jonas Brothers, and later the title role on Sonny with a Chance. Soon after, she started recording tracks for her '08 debut album, Don't Forget. Selena will follow in Demi's footsteps and release a CD this year. "We cried over how happy we are that we're both working in the same place!" says Selena.

Even better? They got to star together in Princess Protection Program. "It was fun working with her," Demi says. Still, nothing beats being BFFs away from the spotlight. "Everyone who 'makes it' has to deal with the same things: people changing, not being able to trust people. But it's okay because I know I have Selena," says Demi. Selena seconds that. "You never know who's your real friend" in Hollywood, she says. "But we can always go back to each other."