Pope Pius IX decreed that the boy could not remain with his Jewish family and he was taken to the Vatican to be brought up as a Catholic. The case caused domestic and international outrage.
"We saw the advert and we thought it would be a good experience," said Nick Woolf, who had come to the audition with his seven-year-old son Toby.
Mr Woolf added: "I did know about the story, and it perturbed me a bit that I had to explain it to Toby. I was slightly unsure whether I should expose a seven-year-old to it. But I doubt he'll be the next Daniel Radcliffe - so we don't have to worry too much!"
Few of the parents were ready to admit they harboured dreams of stardom for their offspring.
Rather, the audition was a pleasant weekend outing at the start of the school holidays.
"It's something to do on a Sunday morning," said Talia Walden, who was there with her son Isaac, aged eight.
One father acknowleged that his eight-year-old, Leo, "isn't really all that into acting, but seeing the name Steven Spielberg in the advertisement made it sound interesting."
Some of the boys, however, saw the morning as something more serious.
Karen said of her seven-year-old, Toby: "Acting is something he's been thinking about and he wants to start the Lamda course at school in September."
A total of 125 boys turned up for the auditions, which a spokesperson from Nina Gold Casting - the agency in charge - described as "really successful".
"We met some really interesting boys and are thrilled with the turnout," she said.
As well as placing an advert in the JC, the casting agency had sought out potential stars by contacting synagogues, and, in at least one case, approaching families in the street.
"We were walking past the Italian church in Clerkenwell and the lady from Nina Gold ran after us and said 'do you want to audition for this Steven Spielberg film?' and gave us a leaflet," said Fran and Justin. Their son Edgar, eight, had attracted attention because of his "darker complexion".
Justin added that the experience was a "big adventure. The fact that we were invited is a big draw. I don't think we would have come otherwise."
The advert had specified that casters were "not looking for highly experienced stage school children", but Justin suspected that some of the boys had been to auditions before.
"Some of the parents are quite familiar with this, and there are children in there bragging of their acting experience and their agents. There are some kids who definitely know what they're doing," he said.
After turning up at 10am the boys had their pictures taken before being moved to another building up the road to play games. From there a shortlist was made with the lucky boys called back for a screen test.
No decision on who might have secured the role is expected yet.
"We're not going to know for months," said the Nina Gold spokesperson, "but auditions will be ongoing until we find him; we'll keep looking where we need to."
