Michelle Obama prepares to blow the whistle at the obstacle course — with Victoria Justice and LeBron James looking on — at Nickelodeon's Worldwide Day of Play on the Mall Saturday. (Amy Argetsinger/The washington Post)

Nickelodeon called it the “Worldwide Day of Play,” but for the VIPs involved in the kid fest on the Ellipse Saturday, it looked a lot like work.

 Teen star Victoria Justice, in exercise gear, was applying yet another touchup of makeup. About 150 specially selected youngsters were rattling thundersticks and shrieking on command for the cameras, in take after take. LeBron James soothed a fussy toddler who really wanted to scamper out onto the made-for-TV fluorescent-painted obstacle course. “I know,” the NBA superstar consoled. “They wouldn’t let me out there, either.”

All were waiting for co-star Michelle Obama to join them for the taping of a short public-service skit. In a feel-good effort to get kids out of the house for some fresh air, Nickelodeon went off the air for three whole hours Saturday and deployed much of its young talent to the Mall.

The first lady taped a ceremonial pulling-of-the-plug with boy band du jour Big Time Rush. (OMG, no, they’re totally different from the Jonas Brothers who, like, no one’s into anymore, stop embarrassing us!) She also turned out to oversee the obstacle course antics (taped to run after Nick went back on the air) – and while Justice’s lines were spelled out on cue cards (“Do you have any tips for training for this obstacle course, Mrs. Obama?), the first lady was simply instructed to “ad lib on Let’s Move initiative.”