Something similar has happened in Game of Thrones.
From the first series, which starred Bean as Lord Eddard "Ned" Stark, it was the youngest member of the Stark clan, Arya, played by then 12-year-old Maisie Williams, who wooed viewers.
Even now, in series four, Williams still steals the show. Sansa Stark, Arya's elder sister, played by Sophie Turner is similarly captivating. The Stark sisters have some of the strongest plot-lines, but their appeal goes beyond the action.
So what's the secret? Casting director Lucy Bevan says the trick is to cast children to be themselves.
"It's a real challenge casting children, and you have to see lots of kids to find the right one. You need to find a child who is as close to the role as it's written as possible to bring it to life truthfully and authentically."
But it all hangs on the quality of the young stars themselves.
Mark Puddle, who runs Westend Stage, a Europe-wide theatre school for children, says: "The main thing is that young people have got better. There are more avenues to train, plus people have learnt more about how to direct children.
"It also helps that entertainment is seen as a serious career now, compared with 20 years ago. There is more confidence in the arts."
- The Independent