The art of Japanese paper-folding beguiles — yet a simple paper crane can’t be constructed without complicated twists and tugs, strong creases and subtle folds.

The challenge of origami has been a mainstay on the opening day of the National Cherry Blossom Festival , the District’s annual rite of spring that started Saturday. But this year, volunteers added another twist. After children and parents labored to craft paper cranes, volunteers asked the families to give them up.

“In a way, we’re encouraging a bit of critical thinking,’’ said Scott Kratz, vice president for education at the National Building Museum, which hosted the festival’s family day. “We encourage them to work hard for this paper crane. And then they have to make a choice: to keep them or to donate?”

The museum is planning to ship the cranes to the Bezos Family Foundation in Seattle, an organization that has pledged to donate $2 to rebuilding efforts in Japan for every paper crane it receives, up to $200,000.

The festival has long been the celebration of friendship between the District and Japan. Diplomats gave cherry trees to the District as an act of goodwill nearly a century ago. The light-hearted, 16-day festival has come to draw 1 million visitors each year, organizers say.

This year, there’s a new emphasis: solidarity. During the event’s opening ceremonies, a moment of silence was held in remembrance of the more than 10,000 people dead and 17,000 missing in the aftermath of the March 11 earthquake and tsunami that hit Japan.

Organizers plan on continuing to raise money for relief efforts, festival spokeswoman Danielle Piacente said.

“With so many people attending our events, we are a good conduit for people to help,’’ Piacente said. “Spring is about renewal and this year, it’s also about rebuilding.’’

Saturday’s event was held mostly indoors at the building museum and without actual cherry blossoms, which have yet to peak.

Eight-foot-tall pink paper lanterns hung from the ceiling as thousands of families milled about, trying on kimonos and building wooden planters.

Christie Senft, the museum’s foundation relations manager, said the staff spent a half-hour on Friday trying to perfect origami techniques. They became teachers Saturday, guiding tiny fingers to accomplish the same thing in about 10 minutes.

Hovering over their tots, parents soon took over, their kids’ hands barely touching the colored slices of paper.

“This part’s a little tricky,’’ Senft instructed, turning and pulling a sliver of the paper to create the crane’s head. One fumbling father was so frustrated that he cursed. When he finally figured it out, he handed the crane to his young son, eager to show off the work. No donation there.

Stephanie Aaronson of Capitol Hill held her 11 / 2-year-old boy in her arms as her 3-year-old daughter, Isabel, follow the instructions.

“Wow, this is not a joke!” Aaronson sighed.

Isabel’s purple construction paper was a little tattered from her attempts, but the shape of a crane eventually emerged.

“Do you want to take a picture with it and then donate it to the people in Japan?” her mother asked. Isabel nodded.

But for a few minutes, the girl ran in circles, holding her crane aloft like a toy airplane.

“I don’t know if she’s going to give it up,’’ Aaronson said, as her daughter faded into the crowd inside.

“Isabel! Come back!”

Isabel returned empty handed and said:

“I did it all by myself!’’

She had made a gift of her first origami piece, leaving it in a tall plastic bin and adding to a kaleidoscope of colorful cranes.