Michelle Obama and the jumping-jack brigade at the White House Tuesday. (Mark Wilson/Getty Images)

When photo ops go awry: Michelle Obama was almost felled by small children Tuesday afternoon and had to be rescued by the Secret Service. But we’re getting ahead of the story. . .

Two years into her “Let’s Move” initiative, the first lady keeps looking for new ways to spread the gospel of healthy eating and exercise. This week it involved National Geographic Kids magazine and 450 local school children on the South Lawn trying to break the Guinness world record for the most people doing jumping jacks in a 24-hour period.

Really, there are records kept for that? Supposedly: 20,500 people jumping for one minute at various spots around the globe. But heck, this stuff is mostly for the kids, anyway. The Jumper-In-Chief was tasked with kicking off the challenge at 3 p.m. sharp.

But nothing at the White House is ever that simple. The kids, all clad in matching blue t-shirts, were in place a hour before the record jump, excited and restless. The “Today” show’s Al Roker tried to entertain. Organizers tried to line them up in 15 rows. “Who’s ready to get into formation?” Ragtag lines zigzagged across the lawn.

The first lady bounced out to squeals from the crowd.

“We’re going to show people today is that moving is fun, right?” she exhorted.

Yeah!!! The kids were all ready to jump their little hearts out. . . but the official countdown clock still had four minutes before they could start. Roker killed time with a game of “Simon Says” and a joke. (“What did the snail say on top of the turtle? Wheeeeee!”)

Folks, it all went adorably downhill from there: Obama began jumping jacks at the stroke of 3 p.m.; the kids broke ranks and pressed around her, some jumping jacks, some just bouncing up and down and mugging for the cameras. At the end of the minute, the tiny mob rushed the first lady. . . and almost knocked her down.

Secret Service agents swooped in while Roker vainly tried to regain some semblance of order : “Everybody get back in line!” Obama never stopped grinning, one kid ran over to reporters and exclaimed: “She touched my hand!

And then it was over. The Guinness record? It will be official at 3 p.m. Wednesday, if anyone is still paying attention.

Video: First lady helps world record attempt