Most common cause of fracture of roof of orbit:

"Orbital roof fractures are very rare as an isolated feature. They are most commonly seen in children following brow trauma. Oxford handbook of Ophthalmology"Fractures of the orbital roof among young children are probably far more common than traditionally has been recognized. There is usually a history of a blow to the brow. Head & neck surgery--otolaryngology By Byron J. Bailey, Jonas T Johnson, Shawn D. Newland 4/e p1346