NarniaWeb points to an article at Mail Online which mentions that Will Poulter from Son of Rambow has been cast as Eustace in The Chronicles of Narnia: The Voyage of the Dawn Treader:
Will Poulter, who has been cast as pain-in-the-butt Eustace Scrubb, the Pevensie children’s cousin, in the next Narnia adventure to go before the cameras – The Voyage Of The Dawn Treader – which Michael Apted will direct.
Awful things happen to Eustace in this tale, but he learns. Will played Lee Carter, the scamp schoolboy in the film Son Of Rambow.
“Voyage of the Dawn Treader” is currently scheduled for a May 7, 2010 release.