(Lisa Buser/AP Photo)

Ever since President Obama inadvertently got in hot water for appearing in a sponsored Samsung selfie tweet with Big Papi, he and the first lady have largely avoided self-shot photos with fans in crowds.

But on Wednesday, in separate cities, the president and first lady relaxed their rules.

"I will tell you in advance that selfies are a little tough," Mr. Obama told members of Congress and their families gathered on the White House South Lawn for the annual Congressional Picnic. "I will make exceptions for little people, but you have to actually be little."

The comment drew laughter, before the president quickly corrected himself: "And I mean young, I don't mean short."

It's not known how many, if any, presidential selfies transpired at the picnic with children of lawmakers (the press corps was quickly ushered out). But we do know the first lady lent her likeness to at least one on Wednesday.

On a visit to St. Jude Children's Research Hospital in Memphis, Tenn., several of the children gathered to meet her asked if they could take a selfie with Mrs. Obama.

"You know what, I don't like selfies, but I'm going to do selfies for you guys, okay? All right," she told the kids. "Because we've already had a good conversation. But we're going to do selfies."

Then, one child raised an urgent and all-important question, prompting the education of Mrs. Obama about the phenomenon of "ussies." From the official transcript:

CHILD: Is that selfie going to be an "ussie?"

MRS. OBAMA: Say that again.

CHILD: Is that selfie going to be an "ussie?"

MRS. OBAMA: We will all do a selfie. (Laughter.)

CHILD: Yes.

MRS. OBAMA: Everyone - we will do -

CHILD: An "ussie."

MRS. OBAMA: An "ussie."

CHILD: It's called an "ussie" when it's more than one person.

MRS. OBAMA: Whatever you guys want to do, is my point. (Laughter.) An "ussie," a selfie, a yousie, a weesie - I don't know. (Laughter.) I will do whatever you guys want.