Which child of a president was on the cabinet of another president?

I think Robert Todd Lincoln, Abe's boy, was in McKinley's cabinet. I am not certain, nor do I know his office.

Doria, you are correct about the child, but not about the president.

Hint: Office was Secretary of War

I think I got confused because of the unusual circumstance of Lincon, the younger. I just know that had I been a president when he was alive, I wouldn't have let him near me.

Following his father's assassination, in May of 1865 he, his brother Thomas (Tad) Lincoln (1853–1871), and their mother moved to Chicago where Robert completed his law studies at the University of Chicago (a school different from the university presently known by that name). He was admitted to the bar on February 25, 1867. On September 24, 1868, he married Mary Eunice Harlan (September 25, 1846 – March 31, 1937), the daughter of Senator James Harlan and Ann Eliza Peck of Mount Pleasant, Iowa. They had two daughters and one son:

* Mary "Mamie" Lincoln: October 15, 1869 - November 21, 1938
* Abraham Lincoln II (nicknamed "Jack") - August 14, 1873 – March 5, 1890
* Jessie Harlan Lincoln - November 6, 1875 – January 4, 1948

The last direct descendant of Abraham Lincoln died in 1985.

In 1877 he turned down President Rutherford B. Hayes' offer to appoint him Assistant Secretary of State, but did accept an appointment to become the US Secretary of War from 1881 to 1885, serving under Presidents James Garfield and Chester A. Arthur.

There is an odd coincidence in regard to Robert Todd Lincoln and presidential assassinations. The night his father was shot, Lincoln was invited to accompany his parents to the theater, but declined. When President Garfield was shot in a Washington, D.C. train station in 1881, he was present at Garfield's invitation. When President William McKinley was shot at the Pan-American Exposition in Buffalo, New York in 1901, Lincoln was present at McKinley's invitation. However, he was not an actual eyewitness to any of these assassinations. After McKinley's death, Lincoln let it be known that he wanted no further invitations from any US president, as three of them had invited him to be present at their assassinations.

In another odd coincidence, Robert Lincoln was once saved by Edwin Booth, brother of John Wilkes Booth, from possible serious injury or death. The incident happened at a railroad station in Jersey City in 1863 or 1864, when Robert was traveling from New York City to Washington, and was recounted by Lincoln in 1909. - Wikipedia