The presence of President Trump's daughter and senior aide Ivanka Trump and son-in-law and top adviser Jared Kushner have become staples in the Trump era. But this week, the president's other three adult children, who have no role in the administration, joined Mr. Trump on his first state visit to the United Kingdom, raising questions about why they were there.

Donald Trump Jr. and Eric Trump, who are handling the president's business affairs while he's in office, as well as Tiffany Trump, showed up at the state banquet and for other parts of the president's visit, with no explanation for their presence from the White House. Eric Trump's wife, Lara Trump, who has spearheaded Mr. Trump's reelection efforts, was also present. One of Mr. Trump's children did not join him -- his only minor child, 13-year-old Barron.

Donald Trump Jr. posted to Twitter on Tuesday, "Buckingham Palace... an incredible experience with Her Majesty The Queen. Truly unforgettable."

Buckingham Palace... an incredible experience with Her Majesty The Queen. Truly unforgettable. 🇺🇸🇬🇧🇺🇸🇬🇧🇺🇸 pic.twitter.com/g1zgp90kg5 — Donald Trump Jr. (@DonaldJTrumpJr) June 4, 2019

It as a backdrop that critics suggested looked akin to a monarchic structure, more than a democratic republic.

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Asked why the president's three adult children who aren't in the administration were on the state visit, and who paid for their travel and related expenses, a White House official didn't address why they were there. "They are personally paying," the White House official responded.

Taxpayers still incur any Secret Service expenses for protecting the president's adult children, but those costs can be incurred whether they are with the president or not.

Former President Barack Obama occasionally took his daughters Sasha and Malia on foreign trips, but they were minors living in the White House at the time.

Mr. Trump's first state visit to the U.K. has been largely ceremonial, with a state banquet, appearances with the queen and outgoing British Prime Minister Theresa May. Mr. Trump and First Lady Melania Trump are also there to commemorate D-Day, with one ceremony on Wednesday and more occasions to remember the invasion on Thursday at Normandy.

On Wednesday night, Donald Trump Jr. and Eric Trump were spotted out and about at a local Irish pub, according to video obtained by the Washington Post. They attended the D-Day ceremonies on Thursday in Normandy.