Failure to Thrive (FTT) in Children By Christopher P Raab, MD, Sidney Kimmel Medical College at Thomas Jefferson University Reviewed / Revised Feb 2023 View Patient Education Etiology Diagnosis Treatment Prognosis Key Points More Information Topic Resources Some Causes of Organic Failure... Essentials of the History... Failure to thrive in children is weight consistently below the 3rd to 5th percentile for age and sex, progressive decrease in weight to below the 3rd to 5th percentile, or a decrease in 2 major growth percentiles in a short period of time.