Kai Corkum from the Ards area was struck by a car on Thursday on the Movilla Road.
A man was arrested at the scene on suspicion of dangerous driving.
The arrests were made by police investigating a group dressed as members of the Ku Klux Klan.
A report of a group dressed as Ku Klux Klan members in Newtownards is widely condemned.
The air ambulance attended the scene of the crash on the Portaferry Road near Newtownards.