Unfortunately, this retrospective PECARN study of children with cervical spine injuries isn't as helpful as one would hope. The authors identified 204 children, 58 of whom were aged less than 7 years, who sustained a CSI and had plain radiographs of the cervical spine performed. Of these patients, 127 patients had a definite injury on plain radiography. 41 additional patients had "possible" abnormalities. Then, 20 films were judged to be inadequate by technique. And, finally, there were 18 adequate radiographs with normal findings who subsequently had a CSI identified. The overall sensitivity, then, was 90% (CI 85-94%) - which compares very similarly to the sensitivity in adults from the 34,000 patients in the NEXUS study.
The authors note that most missed injuries fell into two general categories: they were either subtle and non-morbid, or the patients were altered/intubated/focal neurologic findings. It is probably still reasonable to start with screening plain-film radiography and use clinical judgment to determine when CT may be necessary, but if you're looking for airtight evidence to guide your decision-making, CSI in children is too rare to generate that sort of data.
"Utility of Plain Radiographs in Detecting Traumatic Injuries of the Cervical Spine in Children"