"Personally, I think Henry’s just a really nice guy," says Stevenson of his much-maligned character. "People call him ‘Horrid Henry’ but I think he’s just like any boy of our age.
"The girls think he’s horrid because he doesn’t like them, his parents think he’s horrid because he’s got a perfect brother who makes him look bad, and all the teachers think he’s horrid, but with his mates he’s just a chilled out guy."
Huston shares her praise for the rest of the young cast too. "I have to say, I loved working with the kids. It’s really great to play off their honesty and these kids were so talented. The ‘never work with kids’ rule is a total myth. Of course, they look better than you do," she laughs. "But if you’re willing to endure that hardship"
"Perfect Peter and Moody Margaret were the other key bits of casting to get right," says Niblo. "Ross had a lovely naivety about him, but he was confident, and Scarlett is just a fiery tearaway! You wouldn’t mess with her! The second we saw her we knew we’d found Margaret."
Scarlett Stitt, who landed the role of Moody Margaret, says she never expected to get the part. "The casting director turned up to one of my acting classes and asked me to audition. I thought, ‘Why not?’
"But I never thought I’d actually get it. I kept on getting through until I got the part."
Mathew Horne says the experience of working with the young cast wasn’t just pleasant, but life changing. "I fell in love with Ross Marron, who plays Perfect Peter. Kids have always been an anathema to me and this film changed everything."
Alongside the three young stars was a considerable supporting cast of Henry and Peter’s friends, who together make up the Purple Hand Gang and the Best Boys Club and of course the gaggle of girls who are Margaret’s posse. Each of them has their own distinctive personality. "Getting them right" says Whiteley "was as important to us as the main roles."
"I’ve made some great friends," says Theo Stevenson. "That’s the great thing, and because we knew each other from the auditions, on my first day everyone was there to help me through, so I wasn’t nervous or anything."
"We’re sort of a big family," agrees Tyger Drew-Honey. "I really like Theo, he’s a lovely lad."
Siobhan Hayes, who plays Henry and Peter’s mum in the film, was a child actor herself, at the Anna Scher Theatre in North London.
"When I got a job, I just didn’t think about the work so much. You learnt your lines and it was just so exciting - the people you were working with, the camera, the crew. I think that’s how they see it. They had all their lines learnt and they were really professional."
"What you get from kids is a nice lack of self-awareness," says Horne. "That’s something that develops as you get older. So that’s really refreshing."
"I think you can be a lot franker with kids than you can with adults," explains Moore. "You can just give them a note and they won’t be offended, whereas adult actors tend to want to know why you’re giving a note."
Agrees Richard E. Grant: "The spontaneity of the children, and ability to be utterly ‘in the moment’, is what adult actors strive to achieve. They manage to, seemingly effortlessly."
"They were always so very well prepared," adds Moore. "Ross Marron was particularly funny he would turn up knowing everyone’s lines.
"He’d mouth everyone else’s lines while they were speaking them, so we had to get him to stop that! But that was how he remembered his own lines 0 by just remembering everything!"
Kimberley Walsh had to deal with an even younger member of the ensemble. "The biggest challenge has been working with the six-month-old baby my character has," she laughs.
"They don’t really want to be under the hot lights and can’t take direction. But I love babies, so I’m quite enjoying it! She’s the most perfect little child you can imagine - it’s like she’s a born actress."
"The other nice thing about working with children," adds Huston, "is that they don’t work you all night! You don’t go into 16-hour days. Children have a very tight schedule, but on this film they were very efficient and got a lot of footage out of them every day."
"Scheduling around the kids was the biggest challenge," says Executive Producer Allan Niblo. "In Hollywood you can shoot for 15 or 16 weeks on a kids’ film. Here, we had seven, and that was it.
It was funny on the days we were shooting without children," remembers Moore.
"It was a lot quicker! They were just having such a fun time, but the more of them you had, the longer it took. They were enjoying themselves, and I was always keen to keep that atmosphere on set, because I feel that’ll somehow be reflected in the material."
With that glint in his eye, Theo denies there was any mischief on set from the young cast. "But it was great," he laughs, "because if anyone accused me of anything I could say, ‘Oh, but I’m a method actor, I’m just being Horrid Henry!’"
Horrid Henry The Movie In 3D is out now.