The Obama family, foreground, with Jill Biden and family at the Kids’ Inaugural Saturday night. (Joe Raedle/Getty Images)

The official celebration got started quietly on midday Friday, when the White House hosted some very private and elite receptions for high-level (read: big dollar supporters. But the more public celebration kicked off Saturday night with the “Kids’ Inaugural” — “a fizzy, screamy pop

Katy Perry (Joe Raedle/Getty Images)

concert” at the convention center, reports Chris Richards. Highlights: Usher, breaking it down; Katy Perry “in a star-spangled onesie.” And of course, the Obama ladies in their usual exquisitely-coordinated-but-not-too-matchy attire.

Plus, scads of unofficial parties all over town last night; you can get their vibe from the tweets and Instagrams by our many correspondents on the Inauguration Grid. And tune back later to see who won Dan and Monica’s “Running of the Balls” competition. Judges are still deliberating. . . . More all-day coverage on the Inauguration Live Blog.

And what’s this now? The Associated Press cites a source who says that Lady Gaga will play the private inaugural party for White House staffers on Tuesday.

Looking for Friday’s Reliable Source? Start here: Oprah Winfrey: This time, absent from the Obama inauguration and campaign