She announced that MLB and the MLB Players Association will team with the White House in the Let's Move campaign, which promotes exercise and healthy eating for America's youth.
"To the entire MLB Players Association and all 30 players who agreed to be part of the public service advertising campaigns, it just means so much to these kids to see you guys joining in this," Obama said at Oriole Park at Camden yards, home of the Baltimore Orioles. "Your voice means so much more to them than anything we could say."
After the formalities, dressed casually in a print top, white pants and sneakers, Obama joined members of the Orioles and Tampa Bay Rays in a clinic for kids from local baseball teams. Obama participated in all three stations for about a half-hour, playing catch, throwing grounders and shouting encouragement to the children.
Obama showed she knows her way around a baseball field.
Before the session, she threw a few pitches in the bullpen to Tampa Bay ace David Price and was clearly pleased with her performance. Then, after joining the kids on the field, Obama displayed her defensive prowess, deftly deflecting a high throw from one of the youngsters that was headed toward her face.
Price said the first lady's pitching arm isn't bad.
"She tried her own conventional grip and didn't really throw it where she was trying to," Price said. "Then she tried the four-seam grip, which we're all teaching, and she threw it much better. She did well."
Obama was to return in the evening to take part in the first-pitch ceremony before the Orioles faced the Rays.
The Let's Move campaign, according to Obama, is designed to end childhood obesity "So that kids grow up healthier to pursue their dreams." By adding Major League Baseball to the program, Obama hopes to reach a broader audience through 30 public service announcements featuring players from each team.
The first lady of baseball, Sue Selig, wife of MLB commissioner Bud Selig, thanked Obama "for bringing childhood obesity to the forefront and bringing it national attention."
Minutes before the news conference began, a few rain drops fell from the sky. By the time Obama was introduced, the clouds parted and the sun bore down on the field.
"Kids, I know you are hot out there, (but) truly this is all about you," Obama said. "Everything we are doing is because of you, and it's important for you to know that. ... The truth is lots of kids just aren't getting enough healthy foods and they aren't getting enough exercise."
Former big leaguer Tony Clark, now director of player relations for the MLBPA, said, "Major leaguers are looking forward to working closely with the first lady and Let's Move to find ways to educate children and their parents about how to exercise, eat right and make healthy lifestyle choices.
"As a parent, I know firsthand the challenges facing kids. I understand the powerful lure of television, cell phones, computers and video games. However, it's time for all of us -- kids and parents alike -- to get unplugged and get off the couch."
Pointing toward Price and Orioles outfielder Adam Jones, Obama told the children: "When these players were kids they found a spot that they loved. And they practiced and practiced and practiced until they were better at it than anybody else. And we want you guys to do the same thing. That's why we are here."