"Young Sheldon" and "Big" Sheldon speak

After 10 years starring as the beloved and brutally honest Sheldon on "The Big Bang Theory," Jim Parsons is now also behind the cameras as executive producer and narrator of a new show called "Young Sheldon." The prequel series introduces us to the eccentric scientist as a child, played by Iain Armitage.

In the premiere episode, airing tonight on CBS, the 9-year-old genius goes to his first day of high school.

On "CBS This Morning," Parsons explained that his production company began thinking of a series about a child. "We were going with my nephew, who was 10 – he's 11 now – in Texas. He's very smart. I thought, this is describing a young Sheldon, or it could be."

Parson checked in with "Big Bang Theory" co-creator Chuck Lorre. "I thought, if he has any interest in this I should talk to him about it," Parsons said. "But I didn't think he would. I really thought, they would have thought of this before. They've been building material for it for a decade, anecdote after anecdote of Young Sheldon that Big Sheldon has talked about.  But they jumped at it.

"And what [they've] done with it is really miraculous, in my opinion. It is its own show, its own memory play, origin show."

"I love how you don't refer to yourself as Old Sheldon," said Armitage.

"What do I call myself?"

"'Big Sheldon.'"

 "That's the nicest thing I'll say about myself today, probably — just 'big,' not 'old.'"

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Jim Parsons and Iain Armitage, star of the "Big Bang Theory" prequel series, "Young Sheldon."

CBS News

Armitage, whose father is theater actor Euan Morton (currently playing King George III in the Broadway musical "Hamilton"), had previously appeared in the HBO series "Big Little Lies." His audition tape, recorded at his grandmother's house, blew away "Young Sheldon"'s producers.

"It came sort of as a total shock," Armitage said of the callback about his audition.

Parsons says the character Armitage plays is more than just a short version of his "Big Bang" character.

"It really is its own character," he said. "What you're seeing is how he became what we see in the adult show, and so this is kind of its own creature that [Iain's] portraying here. There are overlaps, but we watch him discover things, like comic books, and his clothes are going to change style as he goes through this. All the things that you associate with Sheldon now, you see how they got there through him."

When asked what it's like to be an executive producer, Parsons said, "I'm very mediocre at it."

"Not true," Armitage said.

"It's very strange and it's taken a lot to get used to, even talking to another actor, in this case, Iain. I've never been someone comfortable giving another actor direction. I don't know what makes any other actor tick, necessarily, and I don't want to break it, or him!"

"I'm not that fragile," Armitage interjected. "I'm fragile, but not that fragile."

"No, you're not actually," Parsons agreed.

The series takes place in 1989. Co-anchor Norah O'Donnell asked Armitage — who wasn't alive back then — what he's learned about the '80s.

"First of all, the clothing sort of took me by surprise," he replied, "because you have a lot of things that would be considered totally outdated and really weird today!"

"Young Sheldon" debuts on CBS and CBS All Access Monday, Sept. 25 at 8:30 p.m. ET/7:30 p.m. CT.

  • David Morgan

    David Morgan is a senior editor at CBSNews.com and cbssundaymorning.com.