did jack kelly exist irl?
I am honored to be receiving this question because it seems to pop up periodically in this fandom every few years
The long answer? Can be quite complicated actually.
More recent sources straight from Disney tend to stick to the story that Jack Kelly was a complete work of fiction, or will passingly own to the fact that he was partially inspired by the real-life strike leader Kid Blink and stop there. However, the Newsies novelization mentions "Jack" as a name borrowed from a real newsboy along with the familiar list of Kid Blink, Racetrack, and David (inspired by "Dave" Simons).
Newsies: a Novel, page 137.
In it's introduction, the official MTI Newsies Production Handbook says that Jack Kelly was inspired by "newsies leaders Kid Blink and Morris Cohen." Morris Cohen was the union president after Kid Blink and Dave Simons stepped down following accusations that they'd turned scab. [Evening Telegram, 27 July 1899, p. 8.]
This is corroborated by Bob Tzudiker and Noni White themselves, who created Jack Kelly in the first place. According to my source, to Bob and Noni, Jack "is an amalgam of David [Simons], Kid Blink, and Morris Cohen" and both of Jack's names (alias and legal name) had no historical basis other than that they wanted the name to sound Irish.
That said, a "Jack" Sullivan and a Jack Kelley did in fact exist...
The New York Daily Tribune, 21 July 1899, p. 10.
Early on in the strike, "Jack" Sullivan is named as being the leader of the Arbitration Committee. A later 1905 Sun article credits Sullivan with organizing and carrying through the newsboys' strike, although in actuality there were several newsboy leaders and "Jack" Sullivan was rarely mentioned in the papers at the time of the strike.
The New York Sun, 2 December 1905, p. 3.
"Jack Kelley" is most notably mentioned in the following 1905 article in which he raises money for the grave of fellow newsboy "Dutch" Johnson.
The New York Tribune, 16 May 1905, p. 10.
While it's a stretch, in my opinion, to say that either or both of these boys "inspired" the fictional Jack Kelly given the aforementioned statements, it may be that "Jack" Sullivan and Jack Kelley influenced the creation of Jack Kelly.
We know that Bob and Noni did copious research and consulted primary sources from the strike, so it is possible that they happened upon a few articles that mentioned "Jack" Sullivan and/or Jack Kelley and those names stuck out to them when it came down to naming their characters. This could explain why the novel says that the name "Jack" was borrowed from a real boy, just to cover all their bases.
If you're interested, I've previously made a post listing the other fictional newsies inspired by real boys which you may find here!