Childhood obesity is no fun. Playing is.

Nickelodeon hopes to drive home this basic but seminal concept Saturday morning when it transforms the Ellipse into the people’s playground for its eighth annual Worldwide Day of Play.

The kids’ programming giant has invested almost $15 million in the kinesiology-centric spectacle. During the six-hour (10 a.m.-4 p.m.) fête, the National Park Service expects to host as many as 65,000 ebullient youngsters with a mix of games, activities and guest appearances by Nick’s pre-pubescent stars.

The party gets into full swing right at noon; that’s when die-hard couch potatoes/Web surfers tuned into the Nickverse will see first lady Michelle Obama switch the network offline. The self-imposed blackout will last until 3 p.m. (“We’re out playing, and you should be too” will be the static scolding.)

Music fans are invited to rock out to the uber-positive jams of the Fresh Beat Band at 11 a.m., while the tween panting should commence promptly at 2 p.m. when boy band du jour Big Time Rush takes the stage for a five-song set.

All activities here in D.C. will be free. And the NPS has followed suit by waiving admission fees at all 394 national parks Saturday.