Clinically important traumatic brain injuries are rare in children. The PECARN study provides decision rules for when to avoid unnecessarily obtaining a CT for children who have suffered head trauma.
For children < 2 years old: <0.02% risk of clinically important TBI
For children > 2 years old: <0.05% risk of clinically important TBI
Kuppermann N, et al. Pediatric Emergency Care Applied Research Network. Identification of childrent at very low risk of clinically-important brain injuries after head trauma: a prospective cohort study. Lancet 2009 Oct 3;374(9696):1160-70.