First Lady Michelle Obama said Friday she is fulfilling a childhood dream by leading the US delegation to the London Olympics.

"These Games especially affected our little house on the south side of Chicago," she told US athletes at their training base in east London ahead of Friday evening's much anticipated opening ceremony.

"My brother and I, we would dream about how one day, if we worked hard enough, we might be able to achieve something just as great for ourselves."

She added: "I still have those same feelings of pride, excitement and wonder. So being here is otherwordly for me. I'm still so inspired by you and I'm still in awe of everything you have achieved."

She said the Games had a particularly poignant meaning for her family when she was growing up, as her father had watched the events avidly when his battle against multiple sclerosis ended his own ability to play sport.

"In a matter of several years he went from a man who was once a thriving competitor -- he was a boxer and swimmer throughout high school -- and then he was stripped of all of his hopes," she told the US team.

The First Lady, who campaigns against child obesity, said she hoped watching the US athletes would encourage children at home to "get off the couch".

"Our goal is to get all kids in our country and across the world in a better state of health, and that starts with getting up and moving," she said.

"As you all compete here, think of your fellow competitors back home -- all those young kids who are going to be thinking of visions of you as they go spike a ball or put their toe in that first water."

She said she hoped the US athletes would have fun in London, but added, "Winning is good."

The First Lady, who will be attending the opening ceremony, told the team: "You've got a country back home that is rooting for you every single second, so you've already won."

Ahead of the ceremony, Obama was due to host a sporting event at the US ambassador's residence in London for around 1,000 US military children, along with US and British students.

Her arrival in London comes a day after Mitt Romney -- the Republican who will challenge her husband Barack Obama for the presidency in November -- had to backtrack after questioning whether London was ready for the Games.

Watch the video, uploaded by the Associated Press on July 27.