At a Hunting Park gymnasium, the first lady urged more communities to commit to her two-year-old "Let's Move!" effort to combat the child obesity epidemic and encourage healthy eating and fitness, especially for young people.
She credited local leaders' support for progress made in the 'Let's Move' initiative combating childhood obesity.
"Many of the best solutions start in our city halls or our towns or county councils," said Obama. "They start with leaders like the men and women on stage who see peoples' struggles up close."
She was joined at the Lenfest Police Athletic Center by nine mayors - including Philadelphia Mayor Michael Nutter and Newark, NJ Mayor Cory Booker - and other elected officials from around the country who have implemented anti-obesity changes in their municipalities.
The U.S. Conference of Mayors is having its annual leadership meeting in Philadelphia.
Mrs. Obama was also joined by U.S. Secretary of Health and Human Services Kathleen Sebelius, who announced the next chapter of 'Let's Move' to get more cities and towns involved in promoting healthy eating and exercise. She said the effort is vital.
"Because when we talk about our children's future, we talk about our nation's future," Sebelius said.
Kids at Wednesday's event also got to play with a new KaBoom playground. And many are taking the first lady's visit and her message to heart.
"I am excited that she came," said 10-year-old Jeremy Jackson. "I think if you live healthy, then I think you live longer. You have to stay fit and can't be in your house all day."
"Exercise, eat vegetables and jog with my dad," said 11-year-old Najee Melton.
The Robert Wood Johnson Foundation has provided a $1 million grant to kick off a new component of the "Let's Move!" initiative. A new website, healthycommunitieshealthyfuture.org, went live Wednesday.
The funding also will assist communities in reaching more children, promoting wholesome food in schools, getting kids more physically active and educating adults about good nutrition and proper portion sizes.
Other organizations involved with the effort are the National League of Cities, U.S. Conference of Mayors and the National Association of Counties. Federal health and agriculture agencies and nonprofits also are expected to help.
The Associated Press contributed to this report.