Pediatric head trauma: abuse or not?

Your pager sounds at 3 am. You're called to admit a 4-month-old infant who sustained a temporal skull fracture. As the overnight pediatric hospitalist at a community hospital, you're asked to admit this child to observation. The fall was unwitnessed and the floor is hardwood. He vomited twice afterward. Head computed tomography scan reveals no additional intracranial injury apart from the skull fracture. A skeletal survey reveals no additional injuries. On examination, you see bruising of the area. The child is sleepy but neurologically intact. The emergency department has called local child protective services, and you wonder what you will tell them when they ask your opinion, especially when the family has no explanation for what happened.