Over the past few weeks I have mentioned TWO mystery roles in HBP. HPANA had this to say:

David Heyman confirmed the casting of two 11-year-old red-haired children for the next film, Half-Blood Prince, which is set to begin filming in September.

The actors — Taylor Triphook (a boy) and Katie Head — will play two new, minor characters who are not culled from JK Rowling’s sixth novel. Heyman did not elaborate further. Harry Potter and the Order of the Phoenix

Thanks HPANA!