The new British comedy 'What We Did on Our Holiday' carries on a fine tradition of lively romps with serious undercurrents, blending a cast of comedy stars and solid actors to create hilariously offbeat characters. But what sets the film apart is its approach to its child stars.

David Tennant [L] and Rosamund Pike [R] in 'What We Did On Our Holiday'
David Tennant and Rosamund Pike led the cast of 'What We Did On Our Holiday'

Writer-directors Andy Hamilton and Guy Jenkin perfected their methods on the long-running UK television sitcom 'Outnumbered', for which they script the adult characters' dialogue but allow the children to improvise based on last-minute instructions just as a scene begins filming.

More: Read our review of 'What We Did On Our Holiday'

For the movie, this means that the grown-ups - among whom were David Tennant, Rosamund Pike and Billy Connolly - get to play the more carefully planned comedy routines, while the kids completely steal the show, because their humour comes from their own personalities. Yes, the three young actors - Emilia Jones, Bobby Smalldridge and Harriet Turnbull - are razor-sharp performers. As they react to the twists and turns of the plot, the film comes to life in ways over-scripted family comedies rarely manage to do.

More: Watch the trailer for 'What We Did On Our Holiday'

"I like the fact it's a film where the adults are behaving very badly and the children are behaving like grown-ups," says Pike, who plays the children's mother. "I found that funny and I found that truthful."

Pike and Tennant, who plays her husband, bonded with the young performers on a day out at Chessington World of Adventures theme park. And after working with them, Pike was left with lingering admiration: "If we could let go of our baggage and be as free as these little people, we'd all be much better actors!"