You may have hated Iain Armitage when he played the evil kid in Big Little Lies but you can’t help loving him as Sheldon Cooper in the hit comedy series Young Sheldon. And in person he’s twice as lovable.

He’s slightly older than the character he plays on TV but that works to his advantage. He’s likely to be playing his pre-adolescence for the next few years.

Apparently success hasn’t gone to his head, but he’s no stranger to it. Long before Big Little Lies, he had appeared on talk shows, upstaging his hosts and earning a reputation for being a precocious theatre critic.

For that he has his father to thank, although he downplays that association. (Iain’s dad is a stage actor and mum works as a producer.)

You play Sheldon Cooper in your new series, which is a spin-off of The Big Bang Theory. Were you a fan of the sitcom and how do you get along with actor Jim Parsons (who plays the adult version of Sheldon on the sitcom)?

He’s an incredible person, and I loved doing the pilot with him. Sadly, he has to do a lot of Big Bang but we do see each other occasionally. Mr Jim, he’s an incredible person to work with, and I like saying we’re the only two people in the world who ever have played Sheldon. He’s a very fun person and I love to hang out with him.

Iain Armitage and Jim Parsons at an event in Beverly Hills, California last year. Photo: AP

How did you get the part?

We live kind of far away in Virginia, and the agency I’m with is based in New York. So, we would do the auditions on tape, and if it’s good they’d send it in. If it’s really good, you get a call back and they might fly you out (to Los Angeles).

So I got a call back, and I flew out here, did the audition. I didn’t get another call back … and then they said, you’ve got the part. And I was, “Oh my goodness”. So it was basically, audition, send it in, call back, do it, got the part.

Your show has been an instant hit and you’re the reason. When did you realise you were suddenly famous?

I don’t really think I’m famous. I think it’s more that my show is doing well. If I hear a lot of people say, “Oh Young Sheldon is really good,” that makes me happy and proud. Young Sheldon is an ensemble show; there’s no real main character, and if one character got taken away it would not be the same.

Iain Armitage

Iain Armitage stars opposite Shailene Woodley in ‘Big Little Lies’. Photo: HBO Asia

When you see your face on billboards, what’s your reaction?

It’s funny because my dog – right now he’s in New York with my dad – but one time me and my dad and my dog Jamie were walking to a grocery store and there’s a sign outside that says, no pets except service animals.

So, my dad said, “OK wait right here, I’m going to be really quick, I’ve just got to get three things.”

And there I was with Jamie, holding him, petting him and kissing him. And he was jumping around sniffing everywhere. So, we were standing right outside, when suddenly this huge bus comes by, it’s seven feet away from us and has this huge sign of me.

And I screamed, “That’s me, Jamie, see, that’s me.” So that was cool.

Do you ever get stage fright?

Actually I don’t really. I don’t know why. I guess I’m just so excited to go out there that I just don’t really take into account that it could be scary.

You’re obviously tutored on the set. Do you miss going to school?

I actually have always been home schooled, but I do like my classes on the set, and I’m looking forward to going back for Big Little Lies 2 where there’ll be a lot of other kids. I don’t think we’ll all be in the same class, but it’ll be good to have a lot of other kids that I can play with and talk with on set.

What do you like to do when you’re not on set?

Well on weekends I usually go to the park and play with my friends. But now we’re done with Season One of Young Sheldon, I have a hiatus, so yesterday I asked my friend Jake if he wanted to come over.

He’s in the show Love Never Dies. I watched his show and I loved it. We went to Sharky’s, which is a restaurant that I love and had a great time. If my friends are busy, I stay at home and just play with my toys.

If you weren’t an actor is there any other profession that interests you?

I love jewellery; I love gems and diamonds and rubies and that kind of thing, and I collect them. I have a brooch, it looks like plastic but it’s actually an emerald. So I could be a geologist or a gemologist.

I also really want to be a magician in Las Vegas. So, I do have a top four things that I could do, gemologist, geologist, magician, actor. Which one will I choose?

How long do you think you’ll be doing this?

Well, The Big Bang Theory has run for a very long time. I would like to do this a long time too. I love being around my set family, my fake family. Everyone is so nice on the show. We never have arguments on set and it’s always, “Hello, good to see you”. “Good morning, how is everyone?”

Do you have a favourite person in the world?

I have some pretty awesome people in my family, but my grandma – who I call Momay – she’s my favourite. She’s always optimistic. I’ve never seen her get sad; always happy, always with a smile.

She’s one of the funnest (sic) people to visit. She lives in Georgia so we get together for the family reunion and for Christmas. The only downside is she lives in Georgia and there’s a lot of wildlife there. You can catch frogs. I like playing with the frogs at night when they all come out.

Me and my cousins will go toad and frog hunting. But my grandma doesn’t allow frogs in her house. That’s the only bad rule that she has – no frogs, snakes, bunnies, turtles or anything that is not a human.

There are exceptions, if it swims and you have it in a very good container – since it won’t hop or fly around the house – you might be able to bring it in. But otherwise no frogs, snakes, toads or turtles or humming birds or tadpoles in the house.