The first lady should be discussing behavioral change, not weight loss, said Laura Collins Lyster-Mensh, an eating disorder activist and executive director of Families Empowered and Supporting Treatment of Disorder (F.E.A.S.T.).
"We've confused health and weight in a way that's very confusing for children and very confusing for parents," Lyster-Mensh said. "When we speak publicly about putting our children on a diet, we start to get into weight stigma and confusing the message to families."
The focus on obesity, Lyster-Mensh said, turns this into an issue of appearances, which does not bode well for children, especially girls.
"There is simply no reason to be pushing children into weight reduction diets, and that's the message parents out there get," Lyster-Mensh said. "Dieting is a gateway drug to eating disorders for those with a biological predisposition to eating disorders."
Some said parents talking about their daughters' weight can have a harmful impact on young girls.
"One of the things I've noticed is that a lot of girls develop an eating disorder because they don't want criticism from their parents," said Jeanne Sager, a reporter who blogs on parenting Web site babble.com, and who herself, struggled with an eating disorder.
"I don't think Mrs. Obama was trying to do anything harmful to her children," said Sager. But talking so openly about her daughters "makes it more or less open season" for criticism on their weight, she said.
Doctors said behavioral changes are key to guiding children to a healthy life.
"Weight is just a marker for behavior. Losing a particular amount of weight does not work well for kids," said Dr. Goutham Rao, clinical director of the Center for Pediatric Weight Management and Wellness at the Children's Hospital of Pittsburgh, and author of "Child Obesity: A Parent's Guide to a Fit, Trim and Healthy Child."
He said that the first lady raised an important issue by pointing out how her pediatrician went about informing her. Talking about the BMI "opens the door for discussion," Rao said.
Rao said giving a personal example helps to convey the message better to others.
"I think it's completely appropriate she raised it and personalized it so that other mothers and fathers can relate to it," Rao said.
"The fact that she made this public, about her own ... modest changes she made was exactly that -- that this is a public conversation about what we're all doing," said Dr. Judith Palfrey, president of the American Academy of Pediatrics, who was present at the event last week. "It's like a neighborhood conversation except that it's national, about how we live."
Childhood obesity is a major issue facing the United States. It is a serious medical condition that affects close to one-third of all children in the country. That means one in three children in the United States is overweight or obese. Blacks have a 51 percent higher prevalence of obesity prevalence compared with whites, according to the Centers for Disease Control and Prevention. Hispanics have a 21 percent higher obesity prevalence compared with whites.
The first lady has made fighting childhood obesity one of her key priorities. She inaugurated the famous vegetable garden at the White House and has encouraged sports and other healthy activities among kids.