The US President appeared suddenly from behind a partition as the visitors admired Hillary Clinton’s First Lady portrait.
His sudden appearance in the Cross Hall of the East Wing sparked loud cheers and applause from the stunned crowd.
He beckoned the children in the crowd forward for a photograph but only one took him up on his offer – 10-year-old Jack Cornish, from Alabama.
Mr Trump and the child posed for photographs beneath Mrs Clinton’s portrait, which was installed in the White House in 2004, three years after her husband left office.
The White House had been closed for tours since the president’s inauguration but resumed them on Tuesday.