Are William Moseley and Anna Popplewell starring in the third Narnia?

Moseley's character of Peter and Popplewell's character of Susan are not featured in the book "Voyage of the Dawn Treader". they were told at the end of "Prince Caspian" that they were too old to return to Narnia. However, sites listing the cast for "Voyage of the Dawn Treader" also list Moseley's name, so it is yet to be seen how Peter will come into the story when he is not in the original book.