When Scottish author George MacDonald titled his 1864 chapter book The Light Princess, he wasn't kidding. In the story, now a new musical at the Arden Theatre, a teenage royal is light on her feet and in her body. She's so light she floats.

She's also light in the head: Her emotional range spans bemused to giddy, and stops there. The story has fancy costumes, special effects, and actors who play instruments. In the cast are a witchy aunt, a befuddled king and queen, and a besotted boy.

All this makes for a light comedy with some deeper implications from the Old City company, known for turning classic children's tales into all-ages productions.

Prolific Philadelphia actor, lyricist, playwright, and storyteller Tony Lawton took a shine to the under-the-radar fairy tale, and then took on prolific composer, actor, music director, musician, and singer Alex Bechtel as a collaborator to set the story to music. Here, Bechtel and Lawton -- who also have parts in the show -- recall how the play came to be, why modern kids might love it, and how two grown men relate to a flouncy girl with a crown and a serious case of the giggles.

How did you fellows come across this princess story?

Lawton: I had adapted a few pieces by C.S. Lewis, who was heavily influenced by George MacDonald. I read a lot of things MacDonald wrote. The Light Princess, I thought, was the brightest piece.

What's the princess' deal?

Lawton: The protagonist can't stop laughing. I thought that would make a great tone for comedy. Then I found out, as we were working on it, the side effect of the curse that puts her in that condition of not being able to take anything seriously is she has no empathy.

Did it feel a bit odd, to be men writing for a young, giggly, selfish princess?

Lawton: No. The problem the princess has is a problem that applies to both sexes. It's the problem of empathy, of self-absorption. The essence of growing up, of becoming fully human, is to learn empathy, to value other people beside yourself. That, to me, is the heart of the story.

The book your musical is based on is 150 years old.

Bechtel: There's never a bad time to tell a story that encourages empathy.

And the actors play instruments and sing?

Bechtel: There is no orchestra for the piece. The actors are the orchestra. I play piano and accompany myself when I'm acting as the evil witch. The actor who plays the king plays the piano. The actor who plays the queen plays the guitar.

I'm proud of the balance of songs that are bouncy and funny and up-tempo, and sonnets that are more introspective and ballad-driven. I'm very excited to see how an audience of all ages interacts with that aspect. I'm not sure if most kids have seen that sort of thing before.

There's also a great deal of onstage sound effects being performed that are very exciting.

The Arden is also known for artful special effects.

Lawton: There's a great deal of stagecraft and magic in the production.

Bechtel: We have characters that swim in a lake with water that rises. We have a baby who flies with a pulley system, and clouds that move in and pull around the princess.

What about those all-important lessons that seem to pervade everything made for kids these days?

Lawton: That's where the empathy comes in. Kids growing up now have a little more danger of isolating themselves with electronics, of falling behind in the development of their social skills.

Bechtel: I spend a lot of time making plays with live music played by people in full view of the audience. It's something I care a lot about as a theater artist. I believe it's absolutely a reaction to the ubiquitous technological takeover of our culture. How gratified I feel, how connected I feel, to a theatrical event where I can see the artists doing their work for me in the same room.
Any chance the princess' giggling problem is contagious?

Lawton: That would be a good problem to have. I hope we have that problem.

The Light Princess plays through June 4 at Arden Theatre Company, 40 N. Second St. Recommended for children 6 and older. Tickets: adults, $34-$36; children and teenagers, $20-$24. Information: 215-922-1122 or www.ardentheatre.org.