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. 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.
As Mr. Trump presides over a White House with unprecedented turnover, he has relied on his children the same way he has for decades — asking them for advice or seeing them as surrogates in the fight against his real and perceived enemies.
On this visit, another family opportunity surfaced: The Kennedys have long occupied the American political culture as the unofficial royal family, but this week, the Trumps appeared to present themselves as the 2019 version.
“He’s surrounding himself with his family in this kind of certainly royal family, prince-and-princesses way,” Gwenda Blair, the author of “The Trumps: Three Generations That Built an Empire,” said in an interview. “Just as traditionally crowned heads surrounded themselves with their progeny, he has surrounded himself with his progeny.”
Privately, White House officials say that some of the Trump children, particularly those working in the White House, see themselves this way. One senior official, who did not want to speak publicly about internal planning, said that Mr. Kushner and Ms. Trump in particular had grown more emboldened with their requests to be accommodated at official events.
About a month before the Europe trip, several members of the Trump family informed the White House that they wanted to participate. (Ms. Trump said on Twitter that she was “joining the U.S. delegation” for the visit.) There were loose discussions of them traveling on Air Force One, but the plane was already packed with government officials and the first lady, Melania Trump. Ivanka Trump left for Britain on Saturday, while Mr. Kushner traveled separately from the Middle East.
The president landed in Britain fresh from a round of interviews in which he expressed opinions about British foreign policy and after firing off a slew of tweets responding to criticism from the mayor of London, Sadiq Khan, by calling him a “stone cold loser.” But if Mr. Trump’s behavior bothered his hosts — including Prince Harry, whose wife, the Duchess of Sussex, was called “nasty” by Mr. Trump just days earlier — it did not seem to show. (The American-born duchess, formerly known as Meghan Markle, was not in attendance.) The reception that the Trump family received was warm, and the royals seemed interested in engaging and charming their guests, British and American officials said.
But unlike the royals, who wage an endless battle to keep Britain’s voracious tabloids at arm’s length, the Trump children shared behind-the-scenes photographs and tweets of their trip.
“It was an incredible honor to meet Her Majesty The Queen, the longest ruling Monarch in British history,” Ms. Trump wrote of the day on Twitter. “Thank you for a warm welcome to the United Kingdom.”
For Mr. Trump’s children, the Buckingham Palace visit was the highest-profile example of a change in presidential plans made to include them, but it was not the only one.
The weekend before President Trump delivered his State of the Union address in February, several of the special guests who had been invited to sit near the first lady were suddenly told that some changes needed to be made.
Instead of sitting with Melania Trump, half a dozen of the 28 guests she had chosen were told that they would have to sit down the hall from the House chamber, in a room featuring a television, chocolates, tissues and White House aides. The newly available seats were then given to two Tennesseans whose sentences had been cut short by Mr. Trump under a criminal justice overhaul effort that his son-in-law pushed for, and to three of the president’s adult children and two of their spouses.
A few days before the event, Mr. Trump was alerted to the lack of seats by one of his children, and Mrs. Trump was told to make room, according to three White House officials.
In the box that day were Ivanka Trump and Mr. Kushner; Tiffany Trump; Eric Trump and his wife, Lara Trump; and Donald Trump Jr. (Donald Jr., a popular Republican surrogate, had offered to get a seat from one of the members of Congress he is close with instead, officials said.) Among those whose seats were gone was Aubrey Reichard-Eline, the mother of Grace Eline, a 10-year-old cancer survivor who was invited because she works to help other children fight the disease. The man accompanying Joshua Trump, a sixth grader who is not a relative but who was invited because he had been bullied at school over his last name, was also moved down the hall.
“I think they just had a lot of people in general,” Ms. Reichard-Eline said in an interview, stressing that she had no qualms about the seating change and that she and her daughter treasured being there regardless of seating assignments. “They ended up focusing on the true guests.”
A White House official with knowledge of the last-minute planning said at the time that the guests for the box were invited a month before the address, with the goal of focusing on extraordinary Americans. That person added that seats were changed at the last moment to accommodate the children per their request.
Despite the complicated dynamics that may arise, many commanders in chief have relied heavily on family members once in the Oval Office. And the complications of an extended family with adult children in a White House is not without precedent.
Ronald Reagan, who carried the distinction of being the nation’s first divorced president, had an at-times complicated relationship with his four adult children, who cycled through varying degrees of familial tension before, during and after his ascent to the White House. But in his White House, where his children did not formally work, some were excluded from certain gatherings where the seating was limited.
“I know that we often intentionally did not include them in some events, in state dinners and things like that, even when they were in town,” said Gahl Burt, the former social secretary for Nancy Reagan.
In other administrations, adult children chose to take on official roles: Franklin Roosevelt appointed his eldest daughter, Anna, to serve as White House hostess. Her closeness with her father often led to clashes with her mother, the first lady, Eleanor Roosevelt.
“They were a wealthy, famous family like the Trumps,” Katherine Jellison, a historian who studies first families, said of the Roosevelts in an interview. She pointed to a key difference: “None of F.D.R. and Eleanor’s children were ever policy advisers.”
One of the best-known daughters of a president, Patti Davis, said that it was important for children to bear in mind their impact on the White House. Ms. Davis was 28 when her father, Mr. Reagan, was elected. In an interview, Ms. Davis described her time as first daughter as a period of rebellion that she regrets. She kept her distance from the White House, and said that the Trump children must appreciate that lines can easily be blurred.
“Choose one role or the other,” Ms. Davis said. “ If you’re going to have your fingers in the campaign and all that, then you don’t get to pull the family card.”