The first lady said her daughters Sasha, 11, and Malia, 13, were pulled in by the beautiful pictures and eventually read "American Grown: The Story of the White House Kitchen Garden and Gardens Across America."
"They couldn't put it down and they started looking through and then they started actually reading it," she said. "Eventually, I got, actually, a thumbs-up."
Mrs. Obama spoke to a bookstore crowd at an anything-but-typical book signing, which required more than 200 attendees to stand in line for hours last week to get a wrist band, then go through security clearance and again line up for a few hours before Tuesday's signing at a downtown Barnes & Noble bookstore. She thanked the groups that were caught up in the rain while waiting.
The book, released two weeks ago, traces the story of the garden on the South Lawn and community gardens around the country.
"They come to the White House, they don't get star struck, they don't look around, they get to work," she said, as the crowd laughed. "They get our garden planted and harvested in a matter of 10, 15 minutes, sometimes 30 minutes. They just get it done."
Washington resident Britta Nelson brought her three daughters— around the ages of the first daughters— to the book signing.
"I'm curious to see and read how she inspires parents, (and) find ways to have parents get their kids excited about healthy foods," she said.
Nelson waited two hours last week for a wristband and three hours before the signing. She said it was a once-in-a-lifetime chance for her children to meet the first African-American first lady of the United States.
George Washington University graduate student Jamila Lewis said she jumped at the opportunity to see the first lady in person.
"As a black girl, I'm just like ... she's so beautiful and wonderful and she represents our country so well," said Lewis, 24, of Alexandria, Va. "She's trying to do so much to help America and I appreciate her doing what she does." Lewis said she was excited to try the book's recipes.
In an interview aired on NPR's "Talk of the Nation" program Tuesday, the first lady said a fast food lifestyle that has evolved over the years has had an effect on children's health.
"The hope is that by starting the conversation with our children," she said, "I find that adults are more inclined to make the changes for their kids more quickly than they will for themselves."
She added: "Parents want to do the right thing. It's just that societally it feels like we're pushing a big heavy boulder up a hill because everything out there is working against the health of our kids."