The Magic Tree House books have whisked millions of readers on adventures to everywhere from ancient Egypt to feudal Japan. Now, the children's time-travel series is embarking on a new destination: the movie theater.

The Japanese animated adaptation, which premiered at the Tokyo International Film Festival, comes to the cinema about two decades after author Mary Pope Osborne was walking past an old tree house and got the idea for the series that has sold nearly 100 million books worldwide.

Osborne had previously opposed selling the adaptation rights to the books, known for their value for teaching reading, history and geography, because she wanted to keep the stories in children's imaginations.

But she was impressed with the vision of the Japanese filmmakers, who visited Osborne and her husband in the United States to show them the script and illustrations for the movie, and felt confident they would make a good film.

We thought they totally captured the spirit of the brother and sister in the story, Osborne told Reuters at the premiere of Magic Tree House on Sunday, the festival's second day.

The heart of the story was so intact that to me, it was just perfect in that way.

The film, produced by Media Factory and set to be released in Japan in January, follows Jack and his little sister Annie, who discover a tree house filled with books in fictional Frog Creek, Pennsylvania. In the early books, Jack is eight years old and Annie seven.

When Jack points to a picture in a book on dinosaurs and the siblings are suddenly transported to prehistoric times, they realize that the tree house is magical and can take them to any time and place in history they wish to visit.

DETERMINED AND COURAGEOUS

Jack and Annie need to summon every ounce of courage as their lives are threatened by everything from a rampaging Tyrannosaurus Rex to marauding pirates.

Osborne visited schools in Japan's tsunami-hit areas last week and said she was moved by the strength of the children, who she couldn't help notice embodied the heroic qualities that she instilled in Jack and Annie.

The characters are so determined and courageous, and resilient and loving at the same time, she said.

Everything I heard about the children there and saw in the short time, it felt so in harmony with that.

Osborne has written about 100 books over a 30-year career and shows no sign of stopping -- or being stopped.

I broke my finger and wrist two years ago and I was literally typing a 'Magic Tree House' like this, she said, mimicking the action of typing painstakingly with rigid hands and two fingers. But I got the whole book done.

She is working on a Magic Tree House book set at a panda reserve against the backdrop of the 2008 earthquake in China.

Osborne's husband, Will, and her sister, Natalie Pope Boyce, pen the non-fiction companion books to the series. The three are also starting an educational program in the United States to give away books to underprivileged children.

It's just a launching pad to learning about the world and getting excited about learning. That's what our mission is, she said. It's always been inspiring. I don't think I'll ever stop.

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