Traumatic brain injury (TBI) remains a significant cause of morbidity and mortality in children despite advances in prevention and mitigation strategies. Transcranial Doppler (TCD) ultrasound measures cerebral arterial circulation and allows for the calculation of pulsatility indices (PIs), which provides an assessment of cerebral blood flow changes. Yet, the use of PIs in children with TBI is not well understood. In this study, we defined the day-to-day (DTD) PI change of the anterior cerebral circulation and describe its relationship with injury characteristics and neurocognitive outcomes in children with TBI. A prospective observational parent study of 42 children, 2 months to 15 years of age, with mild or moderate-severe TBI who had serial TCDs provided data for this analysis. Both the mean and variation of DTD PI change were evaluated in the context of injury severity, injury sidedness, and neurocognitive outcome. In those with a unilateral injury, a larger mean DTD PI change in both the injured and uninjured side was found in those with a worse Glasgow Outcome Scale-Extended Pediatrics score at discharge. A larger variation in PI was associated with a worse neurocognitive outcome, irrespective of injury severity. Therefore, the mean and variation of DTD PI change may serve as a potential cerebral vascular biomarker of ongoing secondary injury. The use of PI measurements in the monitoring of children with TBI may provide clinicians with new diagnostic and prognostic insights to inform therapeutic interventions and recovery strategies. However, a larger prospective study is needed to confirm these findings and elucidate potential mechanistic links between DTD PI and clinical outcome measures. To our knowledge, this study is the first of its kind to evaluate the use of PI changes in cerebral vasculature in pediatric TBI patients admitted to the hospital.