So what's it like being one of the kids in the biggest kids' movie in many a year?
"When we're on the set, we kind of enter our characters, enter the magic world," explains Daniel Radcliffe, who plays Harry. "It has even entered my dreams - in one dream I was playing Quidditch and I actually fell off the broom. If I could have a wish though, I'd get an invisibility cloak so I'd be able to sneak into rock concerts."
Surely that won't be a problem much longer for the young star, who is already preparing for the second film, Harry Potter and the Chamber of Secrets, which goes into production in December.
"I think it's really cool that kids are the heroes in the film, which has famous adult actors in it, too," notes Daniel. "It shows what kids can do.
"My classmates have behaved exactly the way they always have," he says. "I wouldn't have liked them to be at all different towards me, and if it was going to change, it would have changed by now. In fact it's just getting better. I don't go to a normal school and I now get the best results I've ever had."
Ginger-haired Rupert Grint, aged 12, a boy of few words and a huge smile who plays Ron Weasley, says that he "still argues with his brother", and Emma Watson, 10, who seems much like the little English missie Hermione, adds that "no one has treated me any differently and I'm still not going to get out of making my bed at home."
The most challenging scene for Daniel was the mirror scene. "Harry is frustrated and excited, sad and angry and curious, and I had to try to think of a thought to get that across on screen. The Devil's Snare with the vines and creepers was a lot of fun, too."
Emma liked the troll scene because "there were loads of stunts to do", while Rupert enjoyed eating all the sweets and doing the chess scene. "It was a huge set, with dust everywhere," he recalls.
Emma concedes she will be more relaxed and confident next time around, and says she is not too concerned about her future - even if she does seem the ambitious type.
"Some people say when you act as a child, that you can end up at McDonalds by the time you're 15. I'm up for anything, not just acting. I'd climb Mt Everest, whatever, if a film doesn't come around."
Seasoned Tom Felton, 13, plays Harry's nemesis, bad-boy Draco Malfoy, while his hefty henchmen are relative newcomers, round-faced Jamie Waylett, 12, as Crabbe and a surprisingly mature Joshua Herdman, 14, as Goyle.
The boys certainly seemed to have been cast to type, as 12-year-old Matthew Lewis is as timid and unassuming as his Neville in the movie.
"The toad weed on me," Matthew announces in his mousy voice. "I felt comfortable with it until then. They gave me another one and it did the same thing."
"The best place was Snapes' class," recalls Jamie. "It was a really small cave, there was light coming through, with bits of rat and everything in jars, eyeballs, hands, spiders, freaky stuff, weird things, cultures of dry ice that you use to cook up your potions."
Was it all for real? "They said one of them was actually a baby pig," he responds. The more savvy Josh retorts with a laugh: "I think they were winding you up."
Tom initially went for the title role: "At first I thought, 'Let's go for it, let's go for the big thing!'
"But halfway through you'd realise that once you'd got this film that would be everything really. Once you're Harry Potter you can't get out of it, that's it! Wherever you go you're Harry Potter, not Tom Felton any more. I think my part is perfect for me because it's not too big and not too small."By Helen Barlow