Paul Morigi/Getty Images, via Nickelodeon

Nickelodeon’s eight-year-old Worldwide Day of Play is going big time this year.

On Saturday, Nickelodeon, the children’s television network, will for the first time take its annual event to Washington. To be held on the Ellipse, this year’s day of games and activities will bring together more than two dozen of the network’s stars and characters, and will include a concert by the boy band Big Time Rush, stars of the Nickelodeon series of the same name.

The move to Washington stemmed from conversations Nickelodeon had with Let’s Move, the initiative led by Michelle Obama , the first lady, said Cyma Zarghami, president, Nickelodeon Networks.

On the day of the event, Nickelodeon and its Web site will go dark for three hours to encourage children to take part in physical activities. Mrs. Obama is expected to symbolically flip the switch sending the network offline and off the air.

She has been featured on Nickelodeon recently promoting the day and the Million PALA Challenge. PALA, for Presidential Active Lifestyle Award, is an initiative of the President’s Council on Fitness, Sports and Nutrition. Children can earn the award by participating in 60 minutes of physical activity , five days a week for six weeks. The Nickelodeon event, meanwhile, is prominently featured on fitness.gov .

The event is expected to cost Nickelodeon $8 million to $10 million and draw as many as 50,000 people, some of them no doubt hoping to see athletes such as the N.B.A. stars Carmelo Anthony , LeBron James and Dwyane Wade. Nickelodeon’s dozens of other partners for the event include N.F.L. Play 60 and Major League Baseball . About 5,000 people attended last year’s Worldwide Day of Play, in Riverside Park in New York.

Ms. Zarghami said the move to Washington was not related to the government’s campaign to persuade the food industry, including some Nickelodeon advertisers, to restrict how it markets to children and teenagers.

“We’ve spent 32 years establishing ourselves as people who really care about kids,” she said. “For every partner we have, we believe they care as well.”