In advance of the upcoming Olympic games in London, Mrs. Obama hosted a mini-Olympic competition with physical activities for D.C.-area children at American University on Tuesday. The competition is part of her Let's Move! initiative to promote fitness and healthy eating.

Mrs. Obama was joined by Britain's first lady, Samantha Cameron, who is accompanying her husband, British Prime Minister David Cameron, on an official two-day, visit to the U.S. The first lady and President Barack Obama will host the Camerons at the White House for a state dinner on Wednesday.

The two first ladies stopped by about halfway through the students' hour-long workout. They mostly observed, but Mrs. Obama briefly hit tennis balls with the kids before making a few remarks.

-- Msnbc.com wires contributed to this blog post.

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