The New York State attorney general’s office, which last month subpoenaed Donald J. Trump as part of a civil investigation into his business practices, is also seeking to question two of his adult children as part of the inquiry.

The involvement of the children, Donald Trump Jr. and Ivanka Trump, was disclosed in a court document filed on Monday as the Trump Organization sought to block lawyers for the attorney general, Letitia James, from questioning the former president and his children.

The subpoenas for the former president and two of his children were served on Dec. 1, according to a person with knowledge of the matter. Eric Trump, another of Mr. Trump’s sons, was already questioned by Ms. James’s office in October 2020.

The attorney general’s effort to interview Mr. Trump under oath became public last month, but it was not previously known that her office, which has been conducting a civil investigation into the former president’s business practices for almost three years, was also looking to question Donald Trump Jr. and Ivanka Trump.

Mr. Trump’s three elder children — Donald Jr., Ivanka and Eric — have long been deeply involved in their father’s company, the Trump Organization, which each of them joined shortly after graduating from college.

When Mr. Trump became president in 2017, he turned the business over to Donald Trump Jr. and Eric Trump, as well as the company’s longtime chief financial officer, Allen H. Weisselberg. Ms. Trump took an office in the West Wing.

Ms. James’s civil inquiry is focused on whether Mr. Trump fraudulently inflated the value of his assets to secure bank loans and understated them elsewhere to reduce his tax bill.

She has obtained a number of documents related to the inquiry and has scrutinized several of the Trump Organization’s properties, including its Seven Springs estate in Westchester County and the Trump International Hotel & Tower in Chicago.

If Ms. James finds evidence of wrongdoing, she can file a lawsuit. As her investigation is civil, she cannot file criminal charges.

Representatives for Ms. James and the Trump Organization could not immediately be reached for comment.

The legal filing that disclosed the subpoenas on Monday was signed by a judge who presided over an earlier court action brought by the attorney general’s office that forced the Trump Organization to turn over records and Eric Trump to submit to questioning.

Monday’s filing set a schedule for Mr. Trump’s lawyers to move to quash the latest subpoenas, and for the attorney general’s office to respond to any such motion.

Ms. James’s office is also involved in the separate criminal investigation being led by the Manhattan district attorney, Alvin Bragg, who was sworn in on Saturday. The previous district attorney, Cyrus R. Vance Jr., who had been supervising the investigation, left office at the end of the year.

Mr. Weisselberg and the Trump Organization were indicted in July as part of the criminal inquiry and accused by Mr. Vance’s prosecutors of running a tax-avoidance scheme in which executives were compensated with off-the-books benefits. Lawyers for Mr. Weisselberg have said that he will fight the charges in court.

Last month, lawyers for Mr. Trump filed a lawsuit against Ms. James, seeking to halt her civil inquiry and to bar her participation in the criminal investigation. The lawsuit, filed in federal court in Albany, argued that Ms. James had violated Mr. Trump’s political rights and that her actions had been “guided solely by political animus.”

“Neither Mr. Trump nor the Trump Organization get to dictate if and where they will answer for their actions,” Ms. James said in response. Her office has not yet responded to the lawsuit in court.