Alexandrou, 25, was a struggling musician in 2002, when a school employee who was also one of his guitar students asked him to play at an afterschool enrichment program.

"I already knew some nursery songs because I'd wanted to learn the theme from 'Scooby Doo,' " he says.

Alexandrou has since expanded his repertoire to include such standards as "Baa, Baa, Black Sheep" and "Old McDonald Had a Farm." He's also written his own songs: "Reach Up" and "There's a Grizzly Bear Behind You, Run!," whose lyrics instruct students how to move to the beat. His recent CD, Mr. David's First Album, combines classic children's tunes with his own compositions. The CD was nominated for a 2005 Parents' Choice Award.

"I'm introducing live music to kids, so it's very interactive," Alexandrou says of his performance style. "I try to deliver the songs a little differently than your typical 'Twinkle, Twinkle, Little Star.' They're rocked up, with more energy."

Alexandrou uses his performances to introduce students to his favorite band, The Beatles, with such child-friendly songs as "Yellow Submarine" and "Octopus's Garden." He says Beatles music resonated with him when he was a boy.

"I remember 'All Together Now' as being a children's song," he says. "The Beatles have lots of humor in their music. They know how to be really simple in their delivery yet really effective."

Alexandrou, who usually performs for individual classes, recently played his first all-school assembly.

"It's one of the coolest children's shows I've done because there were 175 kids," he says. "I was stopping to let them sing part of a song. I've never done that before."

Mr. David is set to play an even larger venue on June 25, when he'll give a free concert at the Children's Discovery Museum in downtown San Jose. He's also looking to share his music with children outside the South Bay.

"I'd like to go to Portland, Seattle--wherever there are kids who appreciate it," he says.

Alexandrou has grown to appreciate his accidental career.

"The more I do it, the more I feel like I'm around the people I need to make it move forward," he says. "It's a lot more interesting than it was three years ago."

Mr. David will perform June 25, noon-12:45pm, at the Children's Discovery Museum of San Jose, Woz Way at Auzerias Street, San Jose. For more information, visit www.cdm.org.