Obama wore gray pants, with a black cardigan over a black shirt. She paired an oversized, sparkling gray and black necklace with the ensemble.
Wallis, wore a bright pink sweater, tan pants, pink sparkly shoes and carried a purse in the shape of dog.
She has several of the pet purses, telling Ellen DeGeneres last month: "That's my signature."
Obama commented on the young girl's pose, saying "She seems like a grown woman sitting up here."
Wallis was five when she was cast in the film, which is a nominee for Best Motion Picture. She is the youngest actress to ever be nominated for an Academy Award in the Best Actress category.
She was joined at the White House by director Benh Zeitlin and costar Dwight Henry.
The film follows the adventures of six-year-old Hushpuppy, who, with her home in the Bayou facing flooding and her father ill, goes off to find her mother.
Students from Washington D.C. and New Orleans, where the movie was filmed, asked questions of the cast. Several of the kids were wearing Mardi Gras beads in honor of famous New Orleans parade, which took place Tuesday.
Wallis is the latest in a long line of Hollywood stars to bring their Oscar campaign to the nation's Capital. Bradley Cooper of "Silver Linings Playbook" was in town earlier this month to talk about mental health issues while the team behind "Zero Dark Thirty" held a screening of the film at the Newseum in January.