The tour group, including many young children, cheered and screamed as the President popped out from behind a room divider.
Trump called fifth-grader Jack Cornish of Birmingham, Alabama, toward him, gave him a hug, and posed together for a photo. Cornish, 10, appeared to flash an "OK" sign as Trump gripped his shoulders.
"Work hard, everybody, work hard," he said, standing in front of a portrait of former first lady Hillary Clinton.
Trump waved to the group as he walked away.