LOS ANGELES – “Young Sheldon” wasn’t born overnight. “The Big Bang Theory” producers actually toyed with it 10 years ago.

Then, last fall, Jim Parsons (who plays Sheldon) sent executive producer Chuck Lorre an email encouraging the concept. Studio executives chimed in and, in less than a year, it’s on the air, giving “Big Bang” fans a peek at what intelligent, annoying, unyielding Sheldon Cooper was like as a boy.

To separate the two shows, “Young Sheldon” is not taped before an audience and has a distinct, non-CBS comedy look.

“I’m a nervous wreck,” Lorre says. “It’s a wholly different way to tell a story and the working process is very different. It’s much slower, but the end result is something to be proud of, really.”

Iain Armitage plays Sheldon Cooper as a child in "Young Sheldon." CBS

To play Sheldon Cooper as a pre-teen, producers held auditions, looked at tapes and found Iain Armitage, a 9-year-old web-based theater critic and a star of the Emmy-winning limited series “Big Little Lies.” Armitage (who has his own website, “Iain Loves Theater”) taped an audition at his grandmother’s house on an iPhone.

“We looked at it and went, ‘We can’t possibly be this lucky,’” says Lorre. “He was just spectacular.”

Parsons, who’s also one of the show’s producers and its narrator, was equally smitten: “Astonishingly good…he really way.”

Oddly, Armitage hadn’t been a fan of “Big Bang.” “I don’t watch that much TV anyway,” he says. “But it is aimed at a different audience for me. I saw a couple appropriate clips.”

Once cast, he started working with Parsons who filled him in on the nuances of the character. “He was wonderful,” Parsons says of Armitage. “He’s obviously very easy to talk to and we have a lot more in common now than I would have had at the same age as him.”

Parsons says he was very shy as a child and was mediocre in school.

Armitage, however, is extremely outgoing and considers himself a good student. Because he has conducted interviews with Broadway stars (his father, Euan Morton is an actor, his mom, Lee Armitage, is a theater producer), he isn’t one to hold back.

Parsons, however, says his youth was much more solitary. “I had a great time as a child…but I was much more fearful of other people.” Armitage, he says, “will talk to anyone. I still won’t.”

Now, the two are fast friends. To help Armitage play the character, Parsons gave him insight into some of his quirks. Past “Big Bang” episodes have hinted at Sheldon’s childhood. Laurie Metcalf has been on several times as his mother.

To play the role as a younger woman, Lorre looked to Zoe Perry, Metcalf’s daughter, who he remembers running around the set of “Roseanne” when she was 4 or 5.

Perry talked to her mother about the character but “certain mannerisms just come with the territory. Upon knowing I was going to audition for this, I re-watched all the episodes that she was in because I just wanted to be sure that I was in the same ballpark.”

What's a genius like as a child? That's "Young Sheldon," a look at the "Big Bang Theory" character in his early years. Iain Armitage stars. CBS

While “Young Sheldon” will play with time (his father, for example, died when he was young but is a vital character in this show), it will help build to what “Big Bang” presents now.

To link the series, Parsons provides a voiceover that helps inform the audience.

“It’s great fun,” Parsons says of his second job. “It’s unlike anything I’ve done. At this point, it’s still my knowledge of the adult character that’s carrying with me and really focusing on his commentary of the memory that he’s sharing with you. But there’s a whole thing about Iain…this enthusiastic embrace that is all too easily lost sometimes the more you work. It’s such a wonderful reminder, kind of a basic 101 lesson about the enthusiasm and joy with which to embrace these opportunities and roles and scenes.”

“Young Sheldon” airs at 7:30 p.m. Thursdays on CBS.