The first lady also put in a plug for her husband's health care law.
Mrs. Obama appeared in a silly skit with Fallon and comedian Will Ferrell. Then, in a sit-down interview Thursday, told Fallon, who's wrapping up his first week as host of the long-running NBC show, that President Barack Obama and Vice President Joe Biden are getting ready to show America "how they move."
With her signature charm and humor, Mrs. Obama also talked about the challenge of raising two young daughters, ages 12 and 15, in the rarified world of the White House.
"They want nothing to do with us," she laughed.
"They really want normalcy and the White House isn't normal," Mrs. Obama said. "I'll say 'Don't you want to invite your friends over to watch a movie?' They say 'No one wants to come here.'"
She then cautioned that her older daughter turns 16 this summer and is ready to learn to drive.
"Ladies and gentlemen in D.C. —watch out," she warned with a laugh. "Malia Obama on the road. Frightening."
The first lady also took advantage of her national TV audience to talk about her Let's Move exercise and diet initiative.
"What we're asking people to do is show us how you're moving. We want people to Facebook it, Tweet it, Instagram it." She wants to see "how people around the country are moving."
The hashtag is (hash)LetsMove.
If there's enough response, "we'll have a little surprise. The president, and maybe the vice president, will show us how they move," Mrs. Obama said.
She also pitched the Affordable Care Act, encouraging young people to sign up for health insurance before the end of March deadline.
Young adults, she said, can now be covered for as little as $50 a month, "less than the cost of gym shoes."