The first lady is spending a lot of time walking and training the 6-month-old Portuguese water dog who became a member of the president's family last week.
An energetic breed, Bo plays well into the night, as he did on Wednesday.
"It was like 10 o'clock. Everybody was asleep and we hear all this barking and jumping around," Mrs. Obama said. "The president and I came out and we thought somebody was out there. And it was just Bo. He was playing with his ball. And it was like there was another person in the house.
"He's kind of crazy, but he's still a puppy. So he likes to play a lot," she said.
The dog, unveiled last week after months of speculation, was a gift to Obama daughters Malia and Sasha.
"He loves to chew on people's feet," Mrs. Obama divulged to more than 100 children invited to a program marking the annual Take Your Child to Work Day.
Dozens of executive branch employees brought their children and grandchildren to the White House on to see where their parents work and what they do there. Vice President Joe Biden's granddaughter, Maisy, 8, was among them.
In a question-and-answer session with the first lady, several students wanted to know about Bo.
Asked what she does with her free time, Mrs. Obama said she doesn't get much of it.
"Well, right now I'm taking care of this puppy. So I'm doing a lot of dog walking and dog training," she said.
Another youngster asked what would she do if Bo ran away.
"I would be very sad, first of all but ... he has (dog) tags, and hopefully someone would find him and bring him back," Mrs. Obama said.
She said it would be hard for Bo to get off the South Lawn, one of the places he is taken for walks and to play, because it is gated. But if he were to get out, she said, lots of people would try to track him down.
"I think everyone at the White House would probably help go out and find him," she said. "That's why we're working on training him, so that he doesn't run away and he listens when we call him. And so far he's doing OK, so we hope we don't have that problem."