One hundred bored, uniformed children are seated along long dining tables in a drab room. A matronly lady is playing equally drab music on an organ.

Fifty servers enter, each carrying a large silver platter. In precise choreography, they put the platters on the table in front of the children and lift the lids to reveal hundreds of water balloons.

The children can't resist - it's only a moment of seconds before the room explodes in a huge water fight. Balloons fly everywhere, children are on the tables and swinging on the curtains.

The energy in the room mounts to maximum levels and the children start to transform. A girl grows butterfly wings. A boy becomes a huge robot. One child turns into a big ball of candy floss and floats away. Another child turns into a living bouquet of flowers.

Finally, a group of children transform into an energy rainbow and we see these words:

Monoprix Daily Supermarket. Not your everyday everyday.

Our film was going to have a duration of 180 seconds, and we were shooting in just one location, so the faces of the children cast were going to be the stars. They needed to be fresh, engaging, different. And we needed a lot of them - fifty to be exact. They needed to be the same age, and they needed to be able to stand up to the rigour of what was essentially a two day water fight on the shoot.

There were additional challenges with our featured cast - in the film, these are the children who transform into their wildest dreams. The girl who becomes a butterfly, for example - who could we find that could naturally and believably complete that transformation. The same for the boy who becomes a giant robot - which boy could have that kind of look?

We saw hundreds of children and finally arrived at our cast of 50.

As for the waiters, the idea was that they represent the brand, Monoprix. Their appearance needed to be more uniform. And we didn't want them to steal attention from the children, so we chose a group of people that would blend in with each other.

Our final challenge was to cast our Matron - the lady with red hair who is playing the organ at the beginning. We wanted a character actor - someone who would represent an exaggeration of everyday life.

In summary, we feel that this is a film that was defined by the casting. It was the most important element of the production and without a good casting process, and good results, we would not have had a great final product.