Delineation of calibration regions is a key component of the T1w/T2w ratio myelin mapping approach. The existing method implemented in SPM was not designed for pediatric MRI application. We have developed an automated approach that is able to reliably segment appropriate calibration regions in the pediatric populations- the CSF and scalp fat layer. Using two pediatric MRI datasets, we demonstrated reliability of our segmentation method and the low variance of regional T1w/T2w ratios than the existing method. Our proposed calibration method has potential to be implemented in pediatric myelination studies using the whole brain T1w/T2w ratio technique.