Cause of flexible flat foot is predominantly idiopathic but pediatric flexible flatfoot is typically congenital. Neuromuscular disorders, tarsal coalition and prehallux are possible causes and there has been a controversy for diagnosis and surgical treatment guideline. Therefore we present 11-year old male with prehallux and flexible flat foot who was treated with Kidner procedure and subtalar arthroereisis using Kalix endoprothesis and reported good clinical outcome at 2-years follow up postoperatively.