LONDON — When Queen Elizabeth II welcomed the president on Monday for his first state visit to Britain, Ivanka Trump and Jared Kushner watched from a Buckingham Palace balcony. Later, at a state banquet, Eric Trump posed for photographs. During dinner, Donald Trump Jr. tucked into a menu including lamb and halibut as Tiffany Trump chatted with the queen’s private secretary.

“Looking forward to visiting Buckingham Palace for the first time. The U.K. is a very special place (for so many reasons) and it is an honor for our family to be hosted by Her Majesty,” Eric Trump, who runs the Trump Organization with his brother, Donald Jr., wrote on Twitter before the dinner.

They were also present on Tuesday at Mr. Trump’s news conference with the British prime minister, Theresa May, seated in the second row, in front of some of the president’s senior government advisers. The president has also said that his children would join him on a tour on Tuesday of the Churchill War Rooms, and American officials said they might go to Normandy for the French leg of the trip, too.

Whether they had official roles in the visit or not, the extended Trump family seemed to materialize in London overnight — all save the president’s youngest son, Barron, who stayed home. But Monday’s lavish audience with the British royals was the culmination of more than a month of planning by White House officials who have grown accustomed to accommodating President Trump’s children, whether that includes redrawing plans for a state visit or evicting guests from their seats at the State of the Union address.